otherwise specified, descriptions are moving left to right and top to bottom. All characters, unless otherwise labelled, were introduced in Kingdom Come (hereafter referred to as KC).
Page 1. Panel 1. The T-shaped tower is the former headquarters of the Teen Titans.
The line "criminals are a superstitious, cowardly lot" is of course from the origin of Batman.
Panel 2. The great mass of characters in this panel are, as far as I know, new and made-up by Frank Quitely. The characters along the bar, however, are from Kingdom Come. They are:
Trix. Trix is a new character; the card set has this to say about her: "after `Matrix,' a morphing biomechanism." The Revelations supplement adds this:
Weather Wizard. The former enemy of the Silver Age Flash, in the future of KC the Weather Wizard, with his partners and former Rogues Gallery members Captain Boomerang and Captain Cold, owns and runs this bar/rave.
Lobo. The current DC anti-hero, Lobo was portrayed as aging, unshaven, and flabby in the original KC series.
The bar itself was shown in the original series as the main place for the new generation of metahumans to hang out in.
Derik notes that that appears to be Bart Allen, aka Impulse, in the lower left.
Page 2. Panel 1. Vandal Savage is the one of DC's longest-running villains. The KC Revelations supplement adds this about him:
Page 4. Panel 2. The upended character is Manotaur. Manotaur was introduced in KC, and the card set describes him as a "classical Greek myth armed for the future." More can be seen of him in Kingdom: Nightstar.
Panel 3. The character on the ground is Swastika. Swastika was introduced in KC; the card set describes him as a "American militiaman and anarchist." The Revelations supplement says this about him:
Panel 5. The two characters here are Magog and Nightstar. Magog was, of course, one of the central players in the original KC; The Revelations supplement says this about Magog:
Nightstar is the daughter of Nightwing (aka Robin, aka KC's Red Robin) and Starfire, from the Teen Titans. The KC Revelations supplement says this about her:
Nightstar is featured prominently in Kingdom: Nightstar.
Page 5. Panel 1. The character with the mitt is Plastic Man. Plastic Man, the Golden Age stretching hero, was featured only minimally in the original KC series.
Panel 2. One of the more interesting toss-off ideas of KC was that the bar (described as a "rave" in KC #2) had various metahuman bouncers. Plastic Man, obviously, is one of them.
Page 6. Panel 2. The Solomon Grundy mentioned here is a Golden Age villain; the malevolent failed planet elemental, was shown in KC #2 to be as a bouncer in the bar.
Panel 4. Gingold, mentioned here by Offspring, is the name of the soda pop that gave the Elongated Man, DC's other prominent stretching hero, his powers.
Page 7. Panel 1. The name "Micheline" is quite similar to the last name of David Michelinie, a comic book creator, although if this is a deliberate reference it's one I don't quite get. CBoldman suggests that "Mike" was the name of Plastic Man's love interest in his 1960s revival; Bradw8 confirms this, saying that her full name was Micheline DeLute. Tom Galloway points out the similarity between "Micheline" and the rubber-bodied Michelin Man.
Page 9. Panel 2. The characters that Offspring apparently leads in a team will be seen later in this issue.
Panel 3. Still another discrepancy between KC and The Kingdom is the depiction of Mr. Scarlet, who is given a distinctly more criminal twist here than in the original (he was, after all, on Batman's team in KC).
Page 11. Panel 1. The squabble between the Star-Spangled Kid and Stripesy is a reflection of the original, GA pair who reversed the then-common older-partner-and-younger-sidekick dynamic; it only makes sense that a modern or near-future pairing would bicker about top billing.
Another change from KC is the names of the Star-Spangled Kid and Stripesy, who in KC were called Stars and Stripes.
Panel 2. Zatara's backwards speaking is a holdover from the Golden Age, when a large percentage of comic book magicians followed the example of the original Zatara, who spoke their spells backwards - a Fred Guardineer invention which was soon copied by others.
Panel 3. The bar that was Titans Tower is apparently thought of as a "rave," although here on Earth-Prime that word is generally used about a floating party, rather than something stationary.
Page 12. Panel 3. Mark Coale notes that the "Whiz Wagon" originally appeared in the Fourth World issues of Jimmy Olsen.
Page 17. Panel 2. Brainiac, an alien robot, has always been one of Superman's deadliest enemies, and was responsible for shrinking the city of Kandor, the former capital of Krypton. He was referred to in the original KC as having been destroyed by Superman. His ship here is in much the same shape as the current DC Brainiac's ship.
Mark Coale notes that the ship has the Silver Age coloring but the 1980s "Terminator" design.
Thanks to CBoldman; Bradw8; Mark Coale, as usual; Derik; Tom Galloway; J. Russell Pelt.