Very dark movie. And very much plays by the expected rules while (and, usually, by) breaking them. Christian Bale manages a tremendous feat, which is to not be blown off the screen entirely by the supporting performers; this Batman is anything but forgettable. The late Mr. Ledger's performance is everything that has been said, and moreso; he managed to create a villain that veers from funny-scary to just plain scary. As he plays with the minds of the protagonists, so, too, does he do as much with the minds of the audience. With all due respect for Katie Holmes, Maggie Gyllenhall did a better job; she came across with the necessary ballsiness to be believable as a crusading assistant D.A..
Hitchcock talked about creating suspense by showing the bomb and showing the protagonists conversing and not knowing about the bomb. Mr. Nolan has, with the Joker, taken that conceit and turned it on its head, because, even if we were informed about The Bomb (either literal or metaphoric), we could never be sure what The Joker was going to do with it.