A little dissent here: The Dark Knight is an OK movie.
As a piece of cinematic escapism - it was great. It had my (mostly) full attention from beginning to end. But when the credits ended and I started to think about it, there were a ton of quibbles that prevented it from being the great movie I hoped it would be.
(Before I present those quibbles, remember that I do like the movie - I'm just being contrary for the sake of this discussion.)
Unlike iSm, I really liked the Gotham City of Batman Begins. Gotham was never just Chicago to me.
The only thing I didn't love about the Batman from Begins was the squished face made by the cowl and... the growl. In this movie, more squish, more growl. I know it's reminiscent of the Frank Miller Batman, but I was always more of a Neal Adams Batman kind of guy.
The plot. Was there one? Or many? I know the film wanted to be "complex", but the fact that there were several "ticking clock" episodes throughout the movie made for a lessening of overall suspense, IMO.
Two-Face. For a classic Batman villain, he really wasn't much of a menace, was he? He bumped off a corrupt cop and a mob guy, and then threatened the life of Gordon's kid. And then he dies. And nobody remembers him.
Which brings me to: The Ending. Does Batman really need to be the fall guy for Dent's criminal actions? Why couldn't they just blame The Joker? Or any other number of scenarios? He's such a hero, that now he gets chased. Whatever.
And lastly (for the moment), what about the sound mixing? There were important lines of dialog that were all but swallowed up my explosions and the booming soundtrack. I didn't really want to have to strain to hear Gordon's final monologue.
In all... it's a good effort that I will undoubtedly revisit when it comes out on blu-ray later in the year. But for now, I think it pales in comparison to Begins. And yes, Hellboy II is a better "comic book movie".
A final note on Heath as The Joker. It was a wonderfully written part - and Ledger did a fine job with it. Crazy villains tend to be the best parts in drama. I'll bet that, as written, it could have been done just as well by a number of other actors. LSPE and Tom mentioned Johnny Depp. I don't disagree.