(There are no spoilers here).
It is hard to be objective about Heath Ledger's performance, of course, but surely by any standards his portrayal of the Joker shows an actor at the top of his game. I thought all the performances were good, to be honest, though Bale wasn't given much to work with, was he? A thankless, almost risible, role, that I nevertheless think he did a good job with.
My feeling is that Nolan has been watching The Wire, and the first 45 minutes or so were strongly influenced by it, though obviously a blockbuster film can't hope to do more than gesture humbly in that direction. There was a welcome suggestion that the Universe extends before and beyond the confines of the film and its plot. And the plot itself was demanding on the viewer, which is a pleasant change for the superhero genre.
On the negative side, car chases and ultra-tech generally bore me, and I found a lot of the dialogue impossible to understand. I wish I could have turned on subtitles.
However, I like this tendency to spice up the superhero film with an element of 'naturalism' (can I even call it that?), which emphasises how insane it all is.