First of all, Heath Ledger did a great job with the "Joker" - thus he is the one and only "Joker" for me. Though the double did not do so bad, but at the end it was recognizable - the hair, the way of speaking/behaving was obviously not the same. The movie had very unexpected scenes - and new characters might be added to the play(? - like riddler) but some were lost..
< The shimmering light in the dark lapsed of darkness. > :-)
Nevertheless badman is a really tough guy with a very cool way of acting to situations as far as commenting them.
As a rÃ©sumÃ© I think I can tell you that far: It is a must to watch the movie.