It's not that the movie wasn't well done. What I disliked was that it wasn't really Batman. Even more specifically (and perhaps heretically), it wasn't really the Joker. No offense to the late Mr. Ledger.
It seemed to me that this film took excessive liberties with some beloved characters (if a murderous psychopath like the Joker can be called beloved). So much so that, while the acting and writing and special effects and everthing was fine, I think the movie would have been better if the two adversaries were called something other than Batman and the Joker.
For example, in the real Batman universe, the Joker has a backstory, albeit a sometimes murky one. His maniacal grin has never been a collection of scars, as it is in this film. His white skin and green hair have generally been the result of exposure to chemicals. This Joker's resemblance to the comic book character was primarily cosmetic - no pun intended. Also absent was the twisted and dark humor... which is a big part of what makes the Joker the Joker. Ledger's twitchy tongue was creepy and entrancing... but seemed somehow out of place when associated with the character I know as the Joker. But maybe that's just me.
I had much the same reaction to Quantum of Solace. It was an enjoyable movie, but I would have enjoyed it more if it wasn't pretending to be a Bond movie. The James Bond I know is immaculately groomed and never sweats. He's funny, unflappable and has cool gadgets. The QofS Bond was covered in dirt and sweat the entire movie, seemed largely devoid of humor, and apparently misplaced the majority of his cool spy gear.
There's nothing wrong with reimagining characters and retelling old stories. But the retelling needs to be true to the essence of the original, and these two films just weren't.
I realize this is a purely personal opinion. I'm not saying that either movie was bad, and I'm not opposed to reimagining classic characters and stories. But in these two cases, the changes just didn't work for me. Kinda makes me nervous about seeing Wolverine and the new Star Trek movies...
(Having said all that, I loved Michael Caine and Morgan Freeman in Dark Knight.)
Also - not to change the subject, but what's with all the origin movies lately? I mean, Batman Begins was an origin story, so was Casino Royale, so is Wolverine, so is the new Star Trek... Huh. That's an interesting pattern - all these franchises going back to the beginning. I wonder what that's about.