For me, it takes a few re-watches to understand all of the dialogue and details of any movie. In the dark knight, there are so many small things that I noticed in the 1st half of the movie that actually have an affect on the 2nd half. Like how the corrupt cops Two-Face confronts in the end are all cops we've seen earlier in the movie. The dialogue throughout the entire story is so tight and relevant that nothing seems out of place.
And I forgot how well-paced The Dark Knight is too. No scene in the movie feels too long. I love how even the non-action scenes are exciting and important, while the scenes with action feel even more exciting and important.
Also the Joker is perfect. You literally can't top Heath Ledger's performance in a hundred years. Only upon this re-watch have I actually been able to tell Ledger's face from the makeup. But that was only in the interrogation scene. Every other time we see him, its like we're just watching a real-life version of the Joker doing his thing.