(Spoiler-free, I think)
Amazingly, this movie comes painfully close to living up to its hype. It's really, really good. I would not put it in the pantheon of great films, but there is little doubt that it is far and away the best "comic" movie ever made. Not sure if there's a close second.
This review will seem a little negative only because I'm not going to waste time being redundant and pointing out what every critic on the planet has already said: it's dark, compelling, well-acted all around, and not "fun" in the summer movie sense. Everything you've heard is true. I'll mention two pleasant surprises and one big negative.
First, Christopher Nolan got slightly less terrible at filming action scenes! He replaced his technique from Batman Begins – shaking the camera around so the audience feels like they're "in the action" (i.e. nauseous) – with a mildly irritating Michael Bay-style series of rapid cuts. It's not good, but it's a dramatic improvement. They could get someone to film the action better, but then they'd be stuck with all of the idiocy that accompanies those folks. Second, Aaron Eckhart acts like someone other than Aaron Eckhart, Smug Asshole. That's refreshing.
The problem: this was very, very obviously two films. The original plan was to make the third film in the series about Eckhart (Two Face) as the main villain, but instead the writers and director chose to merge that story into the second film. It showed. A lot. The last hour of this film is a condensed version of a third film, and Nolan struggles mightily to A) connect the second act to the first and B) keep the Joker involved in the Two-Face storyline. Several storylines in the film were truncated as a result.
I suppose a second negative is that I have no idea how they're going to milk a third sequel. What could possibly follow this? One big problem with the Batman franchise (as sharply noted by commenter Scott N.) is that the villains absolutely pale in comparison to the Joker. The only other charismatic villain is Two Face and, well, they shot that wad too. Given the gravity of Heath Ledger's and Eckhart's performances, it's going to be nearly impossible for the writers and whatever actors are tasked to play a milquetoasty villain in the next film to keep pace.
OK, last complaint. Christian Bale's "When I Dress Up As Batman, I Talk Like I Am Trying Really Hard to Shit but Failing" voice gets so ridiculous that he's barely intelligible at the end of the film. Seriously, it's so over the top that, among all of the sound effects and music, I couldn't even understand a few of his lines. At this rate they are going to need to subtitle Batman in the third film. Or pump the Caped Crusader with prune juice until he craps. A lot.