Ebert's review of The Last Airbender (they hastily dropped the "Avatar" from the title after you-know-what) strikes blows for good animated features and against the misuse of 3D.
Other people have documented in great detail how M. Night botched the casting to make the movie more Peoria-friendly, and how he squirmed on the hook when confronted with this, with various dodges about racial ambiguities in anime. But in the end the casting doesn't even seem to have been the movie's biggest problem, which is (based on this review and others I've seen which leaked beforehand) that the movie just plain sucks.
Several takeaways for me from all this:
Adding 3D to a movie after the fact is an abomination that may well be even worse than colorizing, and will almost certainly be employed consistently to milk that many more bucks out of a movie that was no good to begin with.
I owe it to myself to watch the TV series.
An anime-style feature-film version of the story would be well worth doing as a way to make up for this.
Based on his track record, M. Night is less a talented director who made some aesthetic mistakes and more an emperor who got lucky and is only just now being stripped naked.