Burton's Batman was a very good movie. It has held up fairly well almost twenty years later, a feat that the Dark Knight may or may not succeed at (personally, I think it will be widely remembered as the better of the two films).
Both movies have their flaws, but I feel that Burton's Batman mistepped in some really horrible ways. First was the abysmally bad use of Prince music. It's a small thing perhaps, and Danny Elfman's rich score helped make up for it, but the "Gotham parade scene" is a really terrible piece of filmmaking. There's something about the scene that seems off - even the sound is badly mixed.
Jack Nicholson was a great Joker - no doubt about it. But is it fair to say he topped Heath Ledger's acting? Jack Nicholson's Joker was essentially Jack Nicholson with clown make-up on. I mean let's be serious, Jack Nicholson, pretty much IS the Joker already, or at least, he is some version of the Joker.
I realize that we are talking opinions here, but Ledger tapped into something much more raw and visceral than what Nicholson was able to do. Of course, whether or not this is just a byproduct of a good script is unknowable, but Ledger's Joker is ultimately more fearsome, intense, and enigmatic.
I'm not sure how one could argue that Ledger's role wasn't deeper than Nicholson's. Burton's Joker is a vengeful clown. Nolan's Joker is an "agent of chaos" - more disturbing, more wicked, more maniacal. His stands as a much better foil to Batman and all that he stands for. Ledger's Joker emphasizes and enhances the heroic nature of Batman - rather than merely providing a source for Batman to revenge his murdered parents.
But the big flaw of Burton's Batman - the one that the film will never be able to escape - is that it kills the Joker. This mistake is it's biggest blunder. It highlights a disconnect from the Batman legacy and reveals the vanity of the filmmakers. It was, in my opinion, a selfish decision.
Ultimately (and oddly), it's hard to compare the two films. Burton's version is very cartoonish and gives us a "happy" sort of psychopath. Nolan's Batman is darker and more realistic, and gives us a Joker that is far closer to the one depicted in "The Dark Knight Returns."
Bob Kane may have always wanted Jack Nicholson to play the Joker, but I'd argue that's only because he never saw Heath Ledger give it a try.
In case it isn't apparent yet, I like talking about movies.