Nolan has darkened the role much like the first couple movies of the run in the late 90's. More than that he has allowed the stories to play out as they should. He has made them real enough, while still staying true to the comic book origins. Nolan respects the source material, which is something that the past run did not do so well towards the end.
Specifically The Dark Knight seems like the perfect second act to the introduction we are given in Batman Begins. We are introduced to two classic villains, Two Face and The joker. I must say that I thought Jack Nicholson's portrayal of the Joker in the original Batman was tremendous. Having said that Heath Ledger's portrayal of the cunning and conniving Joker was absolutely amazing. He captured the Jokers own insanity and brilliance on the screen. It was quite clear why people are discussing Oscar nominations for Ledger. I would also venture to say that this role, which Ledger clearly engrossed himself in, could be the cause for his untimely death. It is an absolute shame. The lengths he went to to in order to become the Joker must have had effects on him, even though it is just acting.
Walking into the theater I had try to lower my expectations for this film. I thought that nothing this summer could beat Iron Man for the top guy movie. I was wrong. That is not to say that Batman is a perfect film, cause there are some issues. My two biggest gripes is that the setting feels very much like Chicago and This thing that Christian Bale does with his voice when he dawns the suit. The Chicago thing gets me. I mean it is so clearly Chicago which is just not right for Gotham. It should be New York, or some unnamed skyline, but it is very clearly Chicago. My second grip is that Bale, how plays an excellent Bruce Wayne, does this thing with his voice when he dawns the cape and cowl. It becomes very low and very grumbled. I just don't think it is needed for the character and it can sometimes make the dialogue difficult to understand.
This is the bottom line. You should see this movie. it is very very very good. Take the time and see it. Oh, and if you are near a cinematic IMAX Theater, see it there. I hear it is amazing.