I saw Dark Knight twice and I really didn't need to see it the 2nd time. Once was enough. Some movies you don't need to watch multiple times. Still, it's probably the best comic book movie I've seen--I can think of only one other movie that competes for that title (Spiderman 2).
I'm not sure if you're joking about the Joker, but I beg to differ. I think it's the best performance I've ever seen in a movie.