Another thing I forgot to add about Jack's Joker is that he doesn't feel as if he is Batman's greatest foe in Burton's film. He just felt like another villain. The Joker is supposed to be the villain that causes so much crap happening to Batman (mentally torturing him in a way). Other than him killing Batman's parents, he didn't affect Batman that much. Once again, this is Burton's fault and not Jack's.
His origin is also done poorly. When he was Jack Napier, he was one person. And after he falls in the vat of chemicals and resurfaces, he is the exact same person that he was before except that he laughs more. To me, that is just bad writing.