With season three just a week away, i am going to try and evaluate season two as a whole. i am only going to focus on the primary storyline, the ballad of Buffy/Angel/Spike/Drusilla.
In cast some people aren't as fanatical as I am, this is the shorthand I am using, and a very brief description of the episodes, including intros and deaths. note--this is only for relatively new viewers who perhaps aren't as familiar with the second season as some of us. Long time fanatics, who have every ep memorized (like me) can skip the run down by clicking here

WSWB--When she was Bad--Season premier, Buffy stops the anointed one (A1) from reviving the master.
SAR--Some Assembly Required--two boys try to assemble a live girl from parts of dead ones.
SH--School Hard--Spike invades parent/teacher night. intro--Spike, Dru. death--Anointed One
IMG--Inca Mummy girl--Xander falls for an ancient mummy. intro--Oz
RB--Reptile Boy--Buffy and Cordelia are offered as sacrifices at a frat party.
Halloween--Buffy and Co. turn into their costumes. intro--Ethan Rayne
LTM--Lie to Me--Buffy's friend from L.A. tries to sell her to Spike in exchange for immortality.
TDA--The Dark Age--A demon from Giles past returns to haunt him.
WML1--What's my Line, part 1--Spike tries to cure Drusilla with a ceremony involving Angel. intro--Kendra.
WML2--What's my Line, part 2--conclusion.
Ted--Joyce's boyfriend turns out to be a psycho robot.
BA--Bad Eggs--a school project involving eggs goes wrong when the eggs hatch.
Innocence or S/I--Surprise/Innocence--(For the sake of this analysis, Surprise and Innocence will be treated as one episode.) Angel loses his soul after sleeping with Buffy.
Phases--Oz is a werewolf
BBB--Bewitched, Bothered, and Bewildered--A spell Xander casts on Cordelia backfires and every girl falls for him.
Passion--Jenny Calendar is killed after she finds a way to restore Angel's soul. death--Jenny Calendar
KBD--Killed by Death--Buffy must face death while sick in the hospital.
IOHEFY--I Only Have Eyes for You--poltergiests of lovers who died in 1955 haunt the school.
GF--Go FishSea Monsters attack the swim team.
B1--Becoming, part 1--the disk with Jenny's spell is found and Angel prepares to destroy the world. intro-Whistler. death-Kendra
B2--Becoming, part 2--conclusion and season finale. Buffy teams with Spike and stops Angel.

Also, the following season one eps are referred to:

WttHM--Welcome to the Hell Mouth--series premier, the Master tries to rise via the harvest. intro--all main characters, Master, Darla. (WttHM and The Harvest are treated as a single episode)
NKaBotFD--Never Kill a Boy on the First Date--Buffy tries to date, the A1 rises. intro--A1
Angel--Buffy descovers Angel is a vampire. death--Darla
IG--Invisible Girl--an invisible girl terrorized Cordelia
PG--Prophesy girl--season finale, Buffy slays the master. death--Master

Back story--Buffy/Angel Dynamic (B/A). Buffy is intrigued and Annoying with him in WttHM, but in NKABOTFD begins to have fuzzy feelings for him. They intesify in Angel, until they kiss, and he loses control of the demon briefly. While it is likely Joss had no idea what would happen in season two at this time, this is a vitally important clue that should have tipped them off right away--Angel the soul has difficulty controlling Angelus the demon with Buffy. In IG, that Angel loved Buffy was first stated, by Giles, (a dynamic, by the way, which was used far too little in season two.) In PG, Xander stated it as well, and Angel was key to saving Buffy's life. The two left together after the death of the Master, but WSWB found Buffy pushing Angel away. however, at the end she finally broke down in his arms. SAR, Angel admitted he was jealous of the time Xander got to spend with Buffy.
Season Two officially starts with WSWB, however, this episode is really an epilogue to PG. With SAR only forwarding one storyline (Giles/Jenny), season two can truthfully start with the introduction of Spike and Drusilla in SH. WSWB does give some hints into what to expect in the season (as all season premiers do), that is discussing at length on the WSWB review.
The central story line of season two, the Buffy/Angel/Spike/Drusilla dynamic (hereafter B/A/S/D), is begun in SH. We learn that Spike is a powerful vampire, and also an irreverent, boastful one. His slaying of the A1 is rather shocking, because one of the major themes of WSWB was how powerful the A1 was. I'm not sure this was done to show something about Spike, that perhaps he was unimpressed with ritual and prophsesy, or that he was indeed a major threat, or just Joss's was of offing an ineffective bad guy, I'm not sure. However, I was not sorry to see the A1 go. A few things are learned in SH: Spike and Angel have a past, Angel was Spike's sire, and Spike is a bad ass. For the most part SH doesn't advance any stories other than Giles/Jenny, it sets the stage for future eps. We know Spike and Angel had a past, we don't know what it is. We know Dru is insane, we don't know why, and we know she's weak and Spike is trying to cure her of injuries obtained in Prague.
IMG completely ignores the B/A/S/D dynamic, (Spike and Dru aren't guest stars, and Angel is completely missing.) However, RB, while not focusing on it, has a powerful B/A subplot. Angel, not for the first time, warns her of what happens when they go to far. In the wake of Innocence, we wish Buffy has listened. RB is an episode that stands up well over time, especially since I didn't like it the first time I saw it. The giant snake is weak, but it is a major step in advancing the B/A dynamic. For the first time, Angel accepts that maybe it is possible for them to have at least some kind of relationship, and begins to ignore his own warnings. This episode features the second-best B/A scene in the entire series, and features the last Giles/Angel dynamic
Halloween is unique in that it really forwards no major storylines. Buffy has a date with Angel that misfires, Spike and Dru are present, but don't reveal anything, and the B/A dynamic isn't much explored because Buffy has amnesia during the bulk of the show. Apart from introducing Giles dark past and advancing Willow's character, all Halloween did was, in the last five minutes, show that Buffy and Angel are together. However, it does give a glimpse of the 90210 mush that would come to plague pre-Innocence episodes.
LTM remains one of the most powerful, and most revealing eps of the entire season. Most obviously, we finally learn of Drusilla's past and her connection to Angel, and also that her injuries obtained in Prague were the result of an angry mob that supposedly killed her. This vivid reminder of Angel's dark side reminds us why Buffy and Angel should stay apart. For the first time, we see in the crazy Drusilla the fruits of Angelus' exploits.
LTM also gives insight into the Spike/Dru dynamic--Spike gives up all of his prey, and the chance to kill Buffy, in order to save Dru. This devotion to Dru is the most important aspect of Spike's character. It brought him to Sunnydale, and would play a major role in the post-Innocence episodes.
The end is also powerful forshadowing for the direction the series would take shortly: "The good guys are always stalwart and true, the bad guys easily distinguishable by their pointy horns and black hats, and we always defeat them and save the day. No one ever dies, and we all live happily ever after." While Giles is talking about Ford, no one can mistake the foreshadowing in that statement. Furthermore, LTM represents a turning point in the shows writing and style. Before, it had been a clever, exciting, action-packed show, but a light and frothy one none the less. RB had made an attempt at some heavier themes, but it was not successful because the episode itself was lackluster. Even the darker themes of loneliness, explored in NKaBotFD and IG, and death, in PG and WSWB, were overcome, leaving everyone happy. LTM was the first truly dark episode of the season, and it showed a remarkable sophistication and maturity rarely found on television outside of ER, Homocide, or the X-files. LTM showed that Buffy the Vampire Slayer could go places. One last note, LTM marks the first time Buffy tells Angel that she loves him.
TDA attempts another dark episode, somewhat less successful. While the bulk of the episode deals with Giles past (which was not delt with adequitely, I believe,) It did reiterate one of the major themes of the second season--Angel is still a demon. In fact, we gain a small bit of insight on the strength of Angelus--he defeats Eyghon, who obviously was a powerful demon. Interestingly, Angel also reveals a very human side of him in his only other scene, when he agrees to deliver the blood to the hospital. However, even this just shows that he's in control of the demon. Mostly, this episode shows us the Angelus lurks just below the surface, "waiting for a good fight."
For the sake of this critique, WML will be dealt with as one episode. This ep brings to a head the B/A/S/D dynamic, and for all intents and purposes, ends a major storyline, that of Spike's attempt to cure Drusilla. As far as advancing themes, WML is more concerned with action and excitement. Of the central dynamic, we see Buffy is more concerned with Angel than with Drusilla, and that Spike is more concerned with Drusilla than anyone.
It is interesting that WML2 is build as the "episode that would change everything," because it actually didn't change much. Spike and Dru switched places. However, it wasn't so much of a change, but an end- WML can be seen as the end of the first half of season two, and Innocence starts the second half. Nothing actually changes, but paves the way for what is to come.
One last note on WML--After this episode, Buffy and Angel's on again-off again relationship is permanantly on-again. (so long as he remains Angel).
The next episode, Ted, the last before an extending winter break, is a fully filler episode that would have worked better before WML. It definately delved into darker themes of Buffy taking a life, but then copped out by making Ted a robot. Had this episode been placed somewhere else, they could have explored this angle without the robot aspect, but as it was, coming on the heels of major two parter and right before a long break, the producers were unwilling to open a new extended storyline. As it was, Ted advanced two dynamics, Giles/Jenny and Xander/Cordy, but aside from a cute B/A scene did nothing with the principal dynamic, and the characters, apart from Jenny who was able to forgive Giles, really didn't even learn anything.
BA was, when it premiered, not well recieved because of the excess of B/A mush. In the aftermath of Innocence, however, we see how necessary the ep was to advance the B/A dynamic. We saw Buffy and Angel making out instead of hunting, allowing the cowboy vamps to pretty much sit there and watch them. Buffy was ignoring duty for Angel, and, as it turned out, this would be a major fault in Innocence and beyond. A major bit of foreshadowing which few people picked up on--while Buffy and Angel are kissing, the camera pans to a gravestone that says "Rest in Peace."
On the heels of BA comes the Buffy two night event, hereafter just referred to by the second episode Innocence. Surprise, was, in my opinion, too weak to stand on its own and I lump the two together in one blockbuster event. This was the landmark episode in the entire series. No episode in any series ever has so fundamentally changed the themes and dynamics as Innocence. Buffy is divided now into two distinct parts: Pre-Innocence and post-Innocence. The reason--Angel lost his soul and turned evil. Suddenly the theme of Angel and Buffy's forbidden love becomes Angelus is trying to destroy Buffy.
Innocence shakes up every major relationship--Giles/Jenny (the gyspy thing), Xander/Willow (the Cordelia thing), Angel/Buffy (the trying to kill them all thing ), Xander/Cordy (the Buffy thing), Spike/Drusilla (The Angelus thing). One new relationship is formed, Willow/Oz, and an old one is revived, Angelus/Drusilla. Interestingly, In Innocence, Buffy's relationship with every major character save Angel and Jenny, is strengthened by the events. The interaction between her and Xander is better than it's been for a while, and Willow proves to be the best friend you could hope for. Giles proves to be a decidedly parental figure for her, his support at the end is the best moment of the Buffy/Giles dynamic which is explored more fully on the Giles page. Even the Buffy/Joyce relationship, which has been strained at best, begins to thaw a little. This episode also marks the first time in the series that Jenny Calendar plays a part in the major theme, although her role alienates her from everyone else.
Innocence is a turning point, which means a beginning. It begins a new arc, which I call the Innocence-Passion-Becoming (I-P-B) trilogy. Even though more than three eps make up the arc, these three are the principles. Innocence sets the stage for everything that happens for the rest of the season, and in fact, the rest of the series. The resolution of the B/A forbidden love theme, and the tragedy that resulted will always be present in Buffy's mind, no matter how far away from Innocence time progresses. And the theme that began, Angelus' obsession with destroying Buffy, and the way it played out thru the I-P-B trilogy affects and changes the course of all the characters lives. Joss rewrites the rules of television in one of the most daring and heartbreaking eps of this show, or indeed of any show. Very few shows would dare to take one of the most popular characters, make him totally, irreversibly, evil.
Innocence didn't just mark a turning point for the characters, but for the series. LTM proved that BtVS could do an episode in where the central theme was betrayal and learning to deal with it, Innocence made that the central theme of the series. In retrospect, LTM seemed like a test-palate, judging if they could indeed pull off such a marked departure from the standard eps. With LTM being one of the best eps of the season, it is obvious they could. Before Innocence, there was always some ray of hope for a happy ending. Somehow, it would work out for Buffy and Angel. The central theme was them trying to make it work, after all. With Innocence, the theme was learning to deal when your greatest love betrays you. That inherantly darker theme would prevail the rest of the season, and make way for some very dark times.
Two final notes, Innocence marks the return of Spike and Drusilla, but there seems to be some jealousy on Spike's part with the attention she gives Angelus. Many people, including me, correctly predicted a Buffy/Spike paring before the end of the season. Spike was able to cenvey this with a few expressions, kudos to James Marsters for that. Also, in WSWB Buffy challenged Angel to a fight--"come on. you must have wondered what would happen...you the vampire, me the slayer.) Here, that bit of foreshadowing is played out.
Phases was primarily a Willow/Oz episode, which is discussed on Willow's page. However, the central theme of Angelus trying to destroy Buffy is portrayed by the becoming (for those who don't know, "becoming" means becoming a vampire) of Theresa and her attack on Buffy. In LTM, Angel explained that he tormented Dru when he was obsessed with her by killing everyone she cared about. Now, we Angel is starting to work his way in, doing the same thing to Buffy. This episode also continues the Buffy/Xander dynamic which came to the forefront in Innocence.
BBB was very low on B/A, actually, it was very low on Buffy since SMG was hosting SNL when it was filmed, and dealt primarily with the Xander/Cordy dynamic which is detailed on the Cordelia page. However, it served to flesh out the Spike/Drusilla/Angelus triangle. We see an increase in the jealousy on Spike's part, as Angelus increasingly moves in on his territory.
The secord part of the I-P-B trilogy, Passion, is unique in that it is perhaps the only episode of Buffy with no real plot. It is entirely character driven. All the filler eps are, of course, plot related. The eps of the first arc, SH-Halloween-WML are very plot related, LTM's plot is essential to the character and theme developement that makes that ep so successful, Becoming's plot was vital to the episode, and even Innocence, as perfunctory and unnecessary was it was, still had plot. (by plot, I mean monster shows up, Buffy fights it, it goes away.) Passion was solely concerned with furthering the central theme. It is just as necessary as Innocence to the furtherment of the story, which is why the I-P-B trilogy is a trilogy and not an arc--All three eps are vital just as they are. It takes all three of them to tell a single story.
The emotion passion is the actually the major theme in the episode. Angelus is a slave to his passions, we know this because of his obsessions with Drusilla via LTM and we've seen his torment of Buffy. Buffy succumbed to her passions, and lost Angel because of it. In addition, her rage is directed now at Jenny, who did lie to her but was really not at fault for causing Angelus' return. But Buffy needs someone to blame. Giles is caught between the two, but needs to support Buffy more. I would say he is, at least in the beginning of the episode, more devoted to his duty (to Buffy) than his passion (to Jenny).
Drusilla is crazy, so there can be no effective analysis of her. However, two characters in this episode are not controlled by their passions: Jenny and Spike. Despite everything that has happened between them, Jenny is detirmined to make things right. She could walk away, but choses instead to end what she feels responsible for, and bring Angel back. She dies for it, but the fault lies more with Buffy, who left her out alone when everyone she was close to needed protection. Spike also chooses not to let his temper get the best of him, biding his time until he can strike at Angelus. Spike shows amazing patience for the taunts he endures.
The murder of Jenny Calendar is the climax of this episode and the central point of the trilogy. It is the absolute lowest point, because that is the worst Angelus does to her. After it, Buffy begins to control the built up passions that have dominated her since Innocence. It is only after she can control them that she can defeat Angelus and begin to heal.
The idea of being consumed by passion is stated in the episode by Angelus. Jenny is murdered, but not before she completes her task. She controls her passions, and channels it into something useful--finding the curse. Spike escapes the burning warehouse unscathed, and when he finally does make a move it is completely out of the blue (to Angelus) and very successful. Buffy passions lead to the death of Jenny. Giles is consumed by his passions at the end, and nearly killed. Angelus is a slave to his passions, and also nearly killed. But at the end, Buffy is no longer a slave to hers. She controls them now, and in her fight against Angelus is completely driven and focused. She would have killed him then, except she needed to save Giles. Both Buffy and Jenny have passion, but both are able to control them to achieve the desired end. Unfortunately, Buffy learns this too late.
Innocence lays down the groundwork for the trilogy, and Passion sets up the pieces. Everything is now in place for part three to come and knock everything down.
It is interesting to note that each of these characters has a unique interplay with everyone, except Buffy and Drusilla. The initial paring of Spike/Drusilla and Buffy/Angel is broken at Innocence into Buffy and Spike/Angel/Drusilla, but in the course of the Innocence-Passion-Becoming trilogy the dymanics shifts yet again to Buffy, Spike, and Angel/Drusilla. By B2, they've completely switched, Spike/Buffy and Angel/Drusilla. By the end of B2, however, we've come full circle: Buffy/Angel and Spike/Drusilla, not withstanding, of course, the Buffy/Angelparting at the end of B2