Buy this game.
I could pretty much leave this right off at that and it would be all you really have to know. If you're a Batman fan of any kind (especially one of the Animated Series or the comics), then you need this game. It is the single truest representation of the Dark Knight in any game ever.
The graphics are excellent, the music is excellent, the gameplay is excellent - and the writing and voice acting is superb. Kevin Conroy is Batman and Mark Hamill is the Joker. Period.
I have heard some complaints about the villains that were chosen but forget about that- the rogues gallery is perfect. Too many would spoil the pot, not to mention any sequel potential.
Speaking of, I'll take a follow to this asap please. maybe one set in Gotham itself? Little bit of free roaming? Little bit of the cave? Soon? Please?