Let's get this out of the way first thing: You should play this game.
Anyone unfamiliar with the comic book version of Batman (like myself) may think this game to be yet another lame movie licensed tie-in. It isn't. It doesn't resemble Dark Knight in any tangible way other than its high quality production values. The basic gist of the game is this: You've just captured the Joker, and it was a little too easy. You escort him back to Arkham Asylum. You sense something is afoot, so you escort him all the way into the facility just to make sure everything is kosher. Problem is, that seems to have been his plan all along. Long story short, Joker takes over the facility and you've got to find a way to dislodge him, saving various doctors and VIPs along the way.
The way you go about this is through some pretty standard gaming conventions, but Rocksteady has done a really great job with implementation. The stealth parts are stealthier and just plain fun.