I know I'm in the minority on this, but I see The Dark Knight as being mediocre at worst and decent at best.
Batman Begins had such a unique and tangible energy; the dark imagery and direction made for a fantastic movie experience. I thought that the producers of the sequel would have no problem in recreating the magic of Begins, and I went into the movie with high expectations.
I kept waiting for The Dark Knight to really accelerate, but that never happened. While the work of Heath Ledger (and the other cast, to some extent) was excellent, the rest of the film was largely meandering and unfocused. Sadly the movie lacks even in the action department, as poorly executed action and fight scenes are aplenty. Considering today's high standard for quality-shot action, it's hard to believe the makers missed this crucial point. All of this together makes for a sluggish progression of the storyline, and an anticlimactic "climax" and conclusion.
I think part of what made Batman Begins so awesome is that it wove the tale of Batman from a comic book story into a raw and realistic present-day society. It did all of this while still retaining a legendary air to it, and that's what made the first movie so intoxicating and visceral. With The Dark Night, the result is a step back into comic book land. And while this is a place that is (understandably) favored by many a Batman fan, it's a step backward for the quality of the series.