There's no denying that Ledger did an incredible job in The Dark Knight, bringing a whole new level of insanity to the grim/gritty feel that Nolan's trying to create with this trilogy, but the question is was it the right flavour of insanity? Was it the joker's insanity? Most of the comics I've seen with him show him to be far more loving/playful, in a creepy kinda way. His eyes were always wide open, excitable and all, whereas Ledger seemed far more supressed. I was just wodnering every one else's opinion. Personally, I think he did it very well given that they were aiming for a grittier feel, so it may just be Nolan's direction that's responsible for this.