As a rule, I’ve stayed away from M. Night Shyamalan movies ever since The Village. But since The Last Airbender didn’t seem to be a typical Shyamalan flick and because I had a seven-year-old boy asking me to take him, I broke my rule.
My seven-year-old movie buddy was completely engrossed. He loved this movie and walked out of the theater practicing his “Airbender” moves. For me it was just okay. It had a nice environmental message for the kids and borrowed elements from martial arts and Eastern philosophy. But the performances were not very good and the storyline was disjointed, jumping from scene to scene with little cohesiveness.
The movie takes place in a world with four nations: Air, Water, Fire and Earth. In each of these nations, certain people have the power to manipulate or “bend” an element. But only one individual has the power to “bend” all four elements. That person is the “Avatar.” But he disappeared a century ago just as the fire nation launched a brutal war against the other nations, completely wiping out the Air Nation. At the beginning of the movie, the Avatar reappears after being frozen in a kind of state of suspended animation and it turns out he is a boy from the Air nation – the last Airbender – who doesn’t realize he’s been missing for the last 100 years or so.
As the movie progresses, he begins to accept his responsibility as the Avatar and with the help of a young brother and sister from the Water Nation, sets out to restore balance in the world and avoid being captured by the Fire Nation along the way. But this is going to be a long and difficult journey for the young Avatar and this movie is just the first in a trilogy so don’t expect any resolution at the end – expect it to set up part two. 
If you’ve got a young boy who enjoys marital arts and stories about fantasy worlds, or who is a fan of the Nickelodeon animated series, then by all means take him to see it. Otherwise, there’s no reason to go.
Oh and footnote: we saw it in 2D and from what I’ve heard from others who’ve seen it, that’s just fine because it was not originally shot in 3D and was converted after the fact. Apparently, this makes for murky 3D and there have been a lot of complaints about that with this movie.