It's good, not great. A lot is wrong with this film, particularly its overbearing length, which had me squirming in my seat by the 2-hour mark. Sorry, but 152 minutes is too much for this type of movie, a dark (in more ways than one), overbearing melodrama with too many ideas instead of a couple really great ones. The Two-Face storyline is, frankly, superfluous and really deserved its own feature. Aaron Eckhart is good in the role (and the Two-Face makeup is fantastic), but I don't feel the character, as it evolves, belongs here.
Casting is pretty good (I'd like to see Gary Oldman in a Commissioner Gordon movie). It's fun to see Eric Roberts on the big screen again, and casting accomplished actors like William Fichtner and Nicky Katt in small roles gives their characters extra weight in their brief appearances. Maggie Gyllenhaal is, obviously, a big improvement over Katie Holmes in BATMAN BEGINS, but almost anyone would have been.
Visual effects are fine (director Christopher Nolan uses CGI sparingly), music is awful, action sequences confusing and disjointed (Michael Winner could direct a better Batman film than Nolan), effective use of Chicago (even if it is too obviously Chicago we're seeing). Heath Ledger is fine, though nobody would be talking Oscar if the guy was still alive, believe me. He's really doing some Nicholson mixed with Anthony Hopkins and the Cesar Romero laugh. He's a good foil for Batman though.
As usual, the Batman character is kinda weak. Setting aside the stupid voice, Batman comes across as less of a special human, but rather someone who can afford a lot of toys. He does precious little detecting, but why should he, when the writers have handed him gadgets with unlimited power. He might as well as carried Bat-Shark Repellent for all the subtlety the writers show, including the ability to listen to every cellular phone in Gotham City. Not just phone calls, but any conversation taking place near the phone. The movie doesn't give me the impression that Batman is anybody special, but just a guy who has access to super-duper technology (which would tend to narrow the field when it comes to deducing his secret identity).
THE DARK KNIGHT is not the Batman movie I want to see, but, like BATMAN BEGINS, is relatively entertaining before it falls apart beneath the weight of its own self-importance.