I don't want to come off like a nay-sayer, because I really did like The Dark Knight. A lot. I just don't think there was anything particularly Oscar-worthy about it (with the possible exception of Ledger's Joker). To me, everything seemed solid for the scope of the film, but otherwise unremarkable.
The screenplay is tight and involved, but I didn't find it particularly profound or resonant. I get the whole "terrorism" angle, which I don't think was any kind of real commentary on terrorism so much as it was a buzzword component to facilitate the Joker and most of the tension in the film. In other words, there wasn't any lasting effect or moral message; it was merely something familiar for the audience to shudder at.
The direction was decent enough given the amount of scenes (some of them highly complex), but I didn't feel that Nolan and crew captured the best performances from their actors, or in some cases, that the characters were sparsely written in the first place. Michael Caine is steadfast as Alfred, of course, but his role was somewhat neutered from Begins. Gary Oldman is excellent as Gordon, but has to endure feigning over an underused family, and delivering those terribly cheesy and transparent lines at the end. Christian Bale, having been relegated to a pretty clear backseat in The Dark Knight, infuses what charm he can in Bruce Wayne, but lacks subtlety or believability as Batman. Maggie G. as Rachel Dawes is leagues better than Katie Holmes, but I think her character suffers from the viewer's knowledge that, in the end, Batman would never hang up the cape for anyone.
And Aaron Eckart, try as he might to breathe life into Harvey Dent, just can't seem to break through the "paint-by-numbers" manner in which he is written. I thought with Harvey, there was a lot of telling going on, and not much showing. We're told over and over again that he's Gotham's shining beacon of hope, but we don't get to see much of him in action. We're told that he and Rachel are hot and heavy, but their onscreen connection isn't enough to slash our heartstrings later. And because of that, Harvey's motivation for becoming Two-Face is less a moving display of heartbreak, and more a formality. He becomes Two-Face. We know this. There's no suspense.
Ledger's Joker is faultless, of course, but it's clear to me that the entire film was built around that character's inclusion in the series. He delivers all the best and deepest lines, and compared to the rest of the lot, has the most radiant personality by far. Couple that with a capable and hugely devoted actor like Ledger, and of course he's going to shine.
As for the lesser opportunities for award, I've already said in other threads that I thought the cinematography was only pretty good (not overly impressive or visionary, by any means); and that the editing was more problematic than it ought to have been. I had a few issues with continuity, and other sequences (like the final battle on the construction site) were awkwardly arranged. Someone above called the musical score "haunting," and far be it for me to nay-say Hans Zimmer. It's a fine score. But actually, I felt that Begins boasts the more powerful score, and I only got bits of that score in The Dark Knight.
I'm re-reading this, and it sounds like I'm bashing the hell out of the film. Believe me, I'm not. It's a well-constructed film given its nature as a high-profile comic book blockbuster, and what faults I find can only moderately damage an otherwise fun thrillride of a movie. I just don't think it's got the artistic chops to win awards. It's hard to make superheroes accessible to anyone, especially when there's a certain status quo that must be maintained to appease fans. We expect Batman to ghost criminals and glide around on this cool Bat-cape. We don't expect him to ruminate in monologue on the deep, socially poignant aspects of... well, anything. I know that's a superficial example, but the point is we're talking about a summer blockbuster that knows its limits and does everything well enough that it all comes together and delivers. In other words, I don't even think this film is trying to win awards so much as to be just a fun, competent, modestly emotional summer flick.