Just saw this Sunday.
No disrespect to Ledger, but I think a large portion of the credit for his Joker performance must go to the writers, who gave him some very good material to work with. It wasn't as sharp as I would've liked, but you definitely get the impression that Joker was an agent of chaos at best, and a human piece of filth that wanted to drag everyone down to his level at worst.
That said, Ledger's performance was really good. Not better or worse than Nicholson's, just different...an entirely different take. For my money, they're both terrific acting jobs.
Another thing about the Joker character was that, if memory serves, he's always been, in the comics and the Tim Burton movie, a sicko who literally gets his laughs out of murder and mayhem. Jack Nicholson's Joker certainly fit this mold, but Ledger's...not so much. I left with the impression that the movie would've worked just as well if his character were named The Terrorist.
But that's a small carp. Another is the same one I have with a lot of action films: sometimes the action scenes move so fast you almost don't know what you're looking at. And sometimes the camera just moves too damn much. Halfway through the movie I thought if I saw one more shot where the camera circled around the actors as they talked, I was gonna whoops.
But again, those are minor complaints about a very good film. No superhero movie (that I've seen) has ever had the complex layers of this one. So kudos to Nolan and the writers.
Some fantastic shots, especially those that look like they're "diving" off a skyscraper. And that CGI shot where Joker left the hospital was incredible. In one continuous shot he exits the doors, and by the end of the shot the entire building is going up...without one single trace of where the genuine shot ended and the CGI began. Really, really impressive.
I do have to agree the whole section with Batman's night-vision/monitoring system was the one place where the movie seemed to go off the rails and slid dangerously close to becoming "camp".
Only bad thing about the showing I went to was, the audio mix was horrible. The music was often so loud it drowned out the dialogue. I trust that was the theater's fault, and not the movie itself.
Last point: I talked with friends who've seen the film, and they all agree with me -- it's difficult to say I actually enjoyed this film. I liked it very much, yes...but "enjoyed"? The movie is almost relentlessly downbeat, and (SPOILER WARNING; MOUSE OVER TO READ) at the end, everybody loses. The Joker does, Harvey Dent does, certainly Rachel does, Gordon's friendship with Batman is in peril, Lucius Fox has abandoned him, and Batman himself is now an outlaw and loses the woman he loves, both literally and figuratively. It's a terrible price to pay for protecting the people of Gotham City. I can't recall in recent memory a movie which had such a bummer of an ending.
Again, not that I'm saying the movie was bad, it wasn't...but Jesus, was it depressing.