Saw it this afternoon. I don't have anything coherent to say yet, except that it has not been over-promised. I was luke-warm on Batman Begins, even though I softened somewhat upon second viewing. But Dark Knight is in a totally different class. You can't consider it by the normal metrics of superhero movies. It aspire to, and achieves, the actual level of film. This is Chinatown and Heat rolled into one.
Much more later.
Update: I posted more thoughts here and a long essay, "The Dark Knight Triumphant," here.
32 minutes ago