The long awaited expansion to Starcraft is finally here!!!!  Released on December 18th, 1998, right on time!!!.   It includes full battle.net support for all new features and it includes new units, tile sets, campaigns, and more!  Dark Templar Twilight, Snow, and Desert tile sets are added to add some depth to the situation, along with over 100 new multiplayer maps.  The expansion set also includes 3 new campaigns for single player fun.

Here is a chart of what's new in the unit arena:
Name of Unit  Race Picture of Unit  Unit Statistics Description of Unit
Medic Terran Minerals: 75
Gas: 25
Units: 1
Build Time: 50 
Hit Points: 80 
Attack Type: none 
Range: n/a
Rate of Fire: n/a
Damage Type: n/a 
Attack Power: n/a 
Base Armor Rating: 0 
(upgrade factor: +1) 
The long awaited ability to heal Terran troop units, such as firebats and marines, btw, they are all women. ; )~  They have spell like abilites of:
Heal:  Will repair damage of biological units within range.
Restoration:  This will remove parasites, ensnare, irradiate and plague.  Guess what, it removes lockdown too.
Optic Flare:  Reduces targeted unit site to 1, permanently, BIATCH ; )~.
Buildings Required: Barracks, Academy 
Upgrades: Restoration, Armor, Optic Flare 
Valkyrie Terran
Minerals: 250
Gas: 150
Units: 3
Build Time: 80 
Hit Points: 200 
Attack Type: Area
Range: 6
Rate of Fire: 20 
Damage Type: Splash
Attack Power: 8
(+2 upgrade factor) 
Base Armor Rating: 3 
(upgrade factor: +1) 
Although they removed the afterburner the Valkyrie has a volly of 14 Missles.  This  fierce missile attack a makes this unit a welcome addition to the Terran arsenal.  They are great accompanyment to ground forces to proctet them from air assault.
Buildings Required: Armory, Starport with Control Tower 
Upgrades: Attack, Armor
Dark Templar Protoss  Minerals: 150
Gas: 100
Units: 3
Build Time: 80
Hit Points: 80 Shields, 40 Hitpoints
Attack Type: Melee
Attack Power: 45
(upgrade factor: +3)
Base Armor Rating: 1
(upgrade factor: +1)
An extremely capable unit, the Dark Templar is permanently cloaked with an awesome, hard hitting attack.  Get those detectors up!  Two of these merge to form the dreaded Dark Archon.
Buildings Required: Gateway, Templar Archives
Upgrades: Attack, Armor
Corsair Protoss 150 Minerals
100 Gas
2 Units
Build Time: 40
Hit Points: 60 Shields, 100 Hitpoints, 200 Mana
Attack Power: 5
(+1 upgrade factor)
Damage Type: Normal
Base Armor Rating: 2
(upgrade factor +1)
Trying to round out the Protoss air force, the Corsair offers a short range, air to air "splash" attack.  A great air to air defense.  It has one spell ability called:
Disruption Web:  This renders ground based attack almost useless upon the targeted area.  That includes ground to ground and ground to air.  But units outside the web can fire into the web.  Units inside the web can still use their spell like abilities. 
Buildings Required: Stargate
Upgrades:  Attack, Armor, Mana (Argus Jewel)
Dark Archon Protoss Created by melding two Dark Templar.
Cost: 2 Dark Templar
No Attack
Hit Points: 200 Shields, 25 Health, 200 mana
The combination of two dark Templars will simply give you the best spell caster in the game.  It barely has any hitpoints, and has no real attack, but its spells are totally awesome.
Feedback:  This takes the energy points of a unit and converts it to damage.  In other words, if you have a battlecruiser sitting there with 250 Mana, and you cast this, the battlecruiser takes 250 damage. 
Mind Control:  This allows you to take one enemy unit and make it yours.  This unit can be any unit in the game.  Becareful though.  Employing this spell will cause you to loose all your shields, leaving you with only 10 hitpoints and very vulnerable.
Maelstrom:  This causes a group of units in a certain area to be stunned for a short period of time.
Buildings Required: Templar Archives
Upgrades:  Mana (Argus Talisman )
 
Devourer Zerg 50 Minerals
50 Gas
1 Unit
Build Time: 25
Buildings Required: Greater Spire 
Upgrades Possible: Armor Upgrade (Spire)
Hit Points: 250 
Attack Type: Normal 
Range: 6
Rate of Fire: 10
Damage Type: Splash
Attack Power: Hits for1/3 of enemy hp, minimum of 3 damage 
Base Armor Rating: 3 
(upgrade factor: +1) 
A short of splash damage air to air weapon, this unit was toned down from its original design.  Mutating from mutalisks they now shoot out acid spores thats can be used for a nice defense in the air.  These slow flying creatures may seem weak at first but they can become a serious pain in the ass. 
Buildings Required: Greater Spire 
Upgrades: Armor Upgrade (Spire)
Lurker Zerg
100 Minerals
100 Gas
2  Units
Build Time: 30 
Hit Points: 125 
Attack Type: Melee
Range: 6
Rate of Fire: 20
Damage Type: Concussive 
Attack Power: 20
(+5 upgrade factor) 
Base Armor Rating: 1
(upgrade factor: +1) 
Finally a decent defensive unit for the Zerg.  Mutating from hydralisks you can hold down a mine with these units that are capable of attacking when burrowed.  Place them outside your opponents base to stop him from expanding.  If its any type of Zerg defense, this unit is a must.  Although they can't attack when above ground, if burrowed they are deadly.
Buildings Required: Lair, Hydra Den 
Upgrades: Attack Upgrade (Evo Chamber)
Armor upgrade (Evo Chamber)

Some new upgrades:

For Zerg Ultralisks:

Chitinous Plating - Give all Ultralisks an additional +2 to their armor.

Anabolic Synthesis - This will greatly increase the speed of all Ultralisks.

For Terran Goliaths:

Charon Boosters - This will increase the Goliath Air attack range. This does not increase his ground attack range. But it does give the Goliath the range of a Guardian.  Hehe.

And the god damned Protoss don't get shit cause they got the Dark Archon. ; )~