Shit. I was pretty blown away. The first third of the movie will leave you wondering why everyone was raving so much, not because it's bad, but just because it takes a bit to build to full potency. After that, it's like someone grabbed you by the throat and it stays at a fevered, relentless pace for the rest of the film. I did have a couple very minor niggles with it, but those aren't a big deal at all, and the believability and grounded aspects of the rest of the movie combine with some "awesome!" moments and pure theatricality to really polish off one of the best movies of this type we've ever seen.
Yes, Heath Ledger is as good as he was given credit for. I don't know if he'll win an award, but if there's any justice left in the world to be paid for worthy accomplishments, he's sure to be nominated. MyD said it, but it bears repeating: great performances all around. Ledger took the show for sure, but everybody holds up their end of the bargain, with some outstanding work by Bale and Eckhart as well. Gyllenhaal is a fine replacement for Katie Holmes I thought, though she didn't have a ton to do in the movie barring a couple good scenes, and Oldman still makes a great Gordon.
As a warning, this isn't as "fun" as the first movie, to be sure, but it feels poignant and necessary. It absolutely exemplifies what I love about fiction and fantasy, and the way I wish it was treated more often - with respect and dignity. Yes, it's a bit ridiculous in concept, and yes, all kinds of unrealistic things happen, but when you treat it seriously and with decent attention to detail, with a dose of real drama and emotion, something simple can become not just emotionally engaging, but inspiring. It was said numerous times in the movies that Batman is a symbol, and after this movie, he's transformed the meaning of that to something real. The Batman of this movie is a symbol, and the social significance of that in our fearful times is as evident here as it was in Iron Man, even though the latter film went after it in a more literal sense.
But no matter how you look at it, Batman is an icon of the screen now in very real fashion, and you absolutely should go see this film.