Now that it's confirmed that the Airbender movie is a stinker, you'll listen to me when I say, please don't go see it.
Instead, watch the original animated series, it's better than you think. Here's my pitch:
First, about humor. While the show is not intended to be non-stop laughs, yes it's for kids, so there is humor, and you'll have to tolerate that 50% of it is silly fart jokes that are beneath you. Conceded. But there are some genuinely funny-for-grownups moments in most of the episodes. Only a little below a typical Pixar movie in jokes.
Next, there are the characters. Yes, they spend some of their time moralizing about the value of friendship and teamwork and blah blah blah. Conceded. But the characters are genuinely likable, interesting, and have depth and growth that makes you want to keep watching. (Especially General Iroh and Toph--- SO AWESOME.)
The art is also excellent: yes it's a cartoon, but the directors make intriguing, cinematic choices for the sets, scenes, shots, angle, and lighting that are superior not only to most TV, but to lots of movies too. Top shelf.
Lastly, the martial art is impressively authentic. The characters have magical powers (Fire-bending, Earth-bending, Air-bending, etc) which are choreographed on real Kung Fu styles--- water-bending is Tai Chi, fire-bending is Northern Shaolin, etc. And the fight scenes are very creative: each battle is full of interesting new moves and innovative tactics, and no two are alike. It is as fresh and interesting as Dragon Ball Z is rote and tedious. Every fight in every episode is a pleasure to watch.
The show is best in season 2, but you'll want to watch seasons 1 and 3 to see how it starts and how it ends (respectively). The whole show is only 3 seasons, with a climactic and satisfying ending, so it won't leave you hanging.
Anyway, hope you enjoy it! (And don't see the live action movie. It's awful and it will spoil the real show, which is actually good.)