The review title for AA on IGN said "Behold, the greatest comic book game of all time!" Not only was I surprised that IGN got something right, but how right they got it.
As a fan of the old animated series, and Batman lore in-general, Arkham Asylum was incredible. Rocksteady really went all out with that game, from the graphics, gameplay, upgrades, story, and even signature voice acting of Kevin Conroy (Batman) and Mark Hamill (Joker).
I'm only expecting better out of AC, especially after I saw some Catwoman gameplay in the interview video before KOFXIII. I try to reserve Day-1 purchases for stellar games; I know Arkham City will be one of them.