The Joker as shown in Batman: The Animated Series (and the animated movie Batman: Mask of the Phantasm) was great. Mark Hamill did a great job portraying him and managed to mix the character's dark and hilarious nature well. That laugh (and all those crazy variations) was awesome and a great trademark of Joker.
I don't know if casting Heath Ledger was the best choice, but he might surprise me with his performance, so time will tell. Even if the interpretation of the character ended up being darker, I hope we'll still see some of that clown stuff he does, and I particularly want to hear the laugh (although I doubt he'll be as great as Hamill was, but who knows).
Two things kind of irked me in Batman Begins. The first was the fight sequences. I know they're supposed to be chaotic and kind of create the sense of fear the criminals feel when they don't know who they're facing, but I was sad that we didn't have some long battle shots, particularly in the final showdown which would've benefited from a better 'view' of the duel.
The other thing that irked me was the score by Hans Zimmer and James Newton-Howard. It hardly had any memorable themes and despite having a sizable orchestra it sounded more of a synth session due to the mixing process. The theme used for Batman was very simplistic, and even if Zimmer and JNH introduced the actual theme in the end, it wasn't a satisfying way of doing it. If they had really wanted to have a Batman theme before he truly establishes himself as an icon, they could've used the route David Arnold used in Casino Royale (which had a new theme for Bond before he becomes the Bond we know; the theme was also based on the actual classic Bond theme which was a nice touch), but instead they chose a more simplistic way. Heck, Danny Elfman, Elliot Goldenthal and Shirley Walker all wrote great themes for Batman, so I would've expected Zimmer and JNH to really nail this one, but instead they failed for the most part. I hope the score for The Dark Knight will be better, though; I haven't lost hope yet, because Zimmer's gang managed to create awful scores for the first two POTC films whereas the third score redeemed the franchise's music, so if the second Batsy film has a bad score, the third might surprise me.
All in all I'm interested in seeing the coming Batman film. I think BB was quite good, on par with Burton's first Batman and Mask of the Phantasm, so I hope the second film will be as enjoyable as BB was.
Some things you see with your eyes, others you see with your heart.