Ledger's performance = overrated.
People don't just suddenly get good just because they kicked the bucket, especially if the bucket was full of drugs.
The Joker is supposed to be funny and aside from the disappearing pencil, I didn't get anymore dark giggles. He's supposed to have all his little tools like the Joker gas and whatnot.
Instead of the Joker being some mildly crazy JOKER, he was just some extremely deranged psychopath man with makeup and no real story. The fact that they chose not to give this Joker a real back story, instead only those little lies he tells about his scars, is an indication of how empty the Dark Knight was.