There's not much I can say about DARK KNIGHT without spoiling anything so I'll keep it short. (Besides, Todd's sent me script pages so I have to familiarize myself with them and get my reference materials together.) DARK KNIGHT was simply incredible. I don't think there was a single moment in the film that I felt like I was watching a movie. It's a testament to Christopher Nolan's genius (yes, genius) as a filmmaker that you are so completely sucked into this film that you actually believe there is a Batman. Ledger's Joker was perfect. He may not look like the Joker from the comics but once you see his performance you won't care. He was the Joker. The thing that Caesar Romero and Jack Nicholson never got (except maybe one scene in Burton's original version) was that the Joker isn't a clown. He may look like one but he's not. He's the Boogeyman. He should be frightening, not funny. And Ledger was just that. Frightening as hell. He's a sociopath with a dark sense of humor and the complexity of his machinations would make a clockmaker envious. He's Hannibal Lechter as supervillain. It's a shame we'll never get to see more of Heath Ledger in this or any other role.
Anyway, that's about all I can say. If you want a nice, spoiler-free review, I think Chris of Chris' Invincible Super-Blog sums it up best here.
One parting thought. If you've seen it, did you also think it totally cool that the mayor of Gotham City was played by Batmanuel?