Page 1, Panel 3 - As stated, Sentinel's powers are useless against wood. Hal Jordan, the Silver Age Green Lantern's weakness was yellow, but the current one (Kyle Rayner) has a power ring with no known weaknesses.
Page 3 - Here we see a full shot of the new Dr Fate. His costume has remained relatively true to the original, with the exception of an 'Egyptian collar', perhaps relating to his history. Also, Starman refers to "The Raven", an old Boris (Frankenstein) Karloff film from Universal (1963).
Page 4, Panels 3-4 - The saying Mordru started: "Birds of a feather flock together" - hence, why he imprisoned the 'Canary' and the 'Hawk'.
Page 5, Panel 1 - Atom-Smasher recognizes the voice of the new Dr Fate. Another clue as to the mystery identity......
Page 5, Panel 3 - Sand turns to rock, and the familiarity of it is mentioned, harkening back to his days as a silicon monster (Creature in the Velvet Cage).
Page 6, Panels 2-4 - Here we see versions of the JSA, from all different realities, including the 'Colonial Society of Justice', the 'Justice Critters' and a medieval version of the JSA.
Page 8, Panel 4 - Mordru mentions Arion, Mage of Atlantis, who was the star of a 35-issue DC series which ran 11/82 - 9/85, plus a 6-issue mini in '92. He originated as a backup feature in Warlord, from #55 - 62. He lived thousands of years in the past, and might have been forgotten but for two continuity links - he was based in Atlantis, and hence eventually written-in as part of Aquaman's history, and apparently, he was retconned as a direct ancestor of Power Girl, to replace her Kryptonian heritage post-Crisis (Credit: Graeme Fitzgerald).
Page 11, Panel 1 - The new Dr Fate traps Mordru in his amulet. But isn't that where Kent Nelson (and company) reside? Perhaps this is a future plot point.......
Page 11, Panel 3 - Hector Hall (formerly Silver Scarab) is revealed as the new Dr Fate! The clues were all there: the appearance of Daniel in #1 (the son of Hector and Fury), the introduction of Scarab (who shares a similar code name to Silver Scarab, and maintains an 'Egyptian' connection), the mention of him being previously dead (#3), and the recognition of his voice by fellow Infinity Inc. members, Nuklon (now Atom-Smasher). For information on why Hector was chosen to be the new Dr Fate, read the second "JSA Returns!" interview with David Goyer.
Page 16, Panel 2 - As mentioned in #1's notes, Hector Hall is the son of Carter Hall and Sheira Saunders, the Golden Age Hawkman and Hawkwoman.
Page 17, Panel 2 - Hector: "My consciousness....drifted through the Dreaming." As noted in JSA #1, Hector did spend time as the Sandman, before being killed by Morpheus, the original Lord of Dreams. Whether or not Hector's time as Sandman is still acknowledged in continuity remains to be seen, but the inclusion of Daniel in #1 seems to suggest so.
Page 20, Panel 1 - Alan nominates Sand for Chairman, as the "perfect candidate.....a link from the past to the present." Sand was never an official member of the JSA in the past - he was just a sidekick to the Sandman - but now he has come to the forefront as the leader. Like Sentinel said, a perfect link.
Page 21 - Sand: "It's happening again! Just like before....." And Sand is gone.......repercussions of JLA #113, perhaps? However, the way Sand words the above sentence suggests he's turned into sand before, which is incorrect. A minor point, but when it happened 'before', he turned into a sand-monster.