The Last Airbender was horrendous! Shyamalan did not do it justice at all. I hope Nickelodeon refuses to collaborate or fulfill any kind of contract with him for two more movies. There were two things that REALLY bothered me.
1. Shyamalan claimed that he wanted to honor the martial arts from the show. Instead he had the actors spend an eternity waving their arms around before any bending occured. The cartoon versions would have obliterated them in the same amount of time.
2. The ending to the first book was huge! Think ocean. At the end of the movie Aang's success equated to nothing more than a puddle. I so want to explain more, but anyone who is even remotely interested in the REAL Airbender would be getting a decent spoiler - I don't want to ruin it.
The choppy part could have easily been fixed if Shyamalan really thought about what was important. The characters needed to bond with each other and the humor was necessary - he really didn't do anything with that at all.
Best character (and even that is pushing it)? Momo.
Best part of the movie? The scenery.
Please look into the series because it's awesome! Don't even watch the movie for free. It's a waste of your time.