It's not the epic masterpiece it's trumped up to be, but The Dark Knight is a genre-transcending comic book movie for certain. Whether or not that's a good thing is debatable; while the film certainly steps beyond it's birth material, it also manages to forget what it means to be a comic book movie, and so it refuses to be any fun. It's also exhausting, not just due to content but volume of content-- about forty minutes of this movie could easily be shaved off without missing a beat.
With the negative out of the way, this is a very, very strong film, and a new benchmark for mainstream super-hero cinema. Curiously, the film is not driven by it's lead, Christian Bale, but rather by Gary Oldman, Aaron Eckhart, and Heath Ledger, who all turn in nuanced and powerful portrayals of their characters. The film is more about these character arcs than a man in a black fetish suit fighting crime; it's about the struggle of the only good man in a corrupt town trying to do the best he can, it's about the fall of a city's champion, and it's about a city bending to one madman's whim. The film is a battle to get through by virtue of the heavy nihilism on display, but despite the flaws it's a rewarding experience.