I'm only vaguely familiar with the original source material, the animated cartoon, so I didn't know what to expect. Two siblings, who live in the Northern lands discover a bald kid that's been frozen for a hundred years in the ice, along with his really weird monster mount which looks sort of like a combination of a buffalo and that salamander creature from THE NEVERENDING STORY. They realize that he's the Avatar, who can unite the different tribes of fire, earth, water and air. The movie is visually interesting and the effects are good, though it's quite unnecessary for there to be a 3-D version since there's nothing grabbing about it. This is more for kids than THE CHRONICLES OF NARNIA. You never see anyone actually getting hurt. Frozen and immobilized, yes, but no physical injury. It's also open-ended, so if it does well I'm sure there will be a sequel in a few years.
Thematically, THE LAST AIRBENDER fits in with M. Night Shyamalan's previous movies, which is interesting. Yes, it is far better than THE HAPPENING, but I think THE OTHERS, UNBREAKABLE and LADY IN THE WATER are far superior.