Speaking as someone who wasn't a militant fan of Nickelodeon's 'Avatar', but always praised its cinematic mastery, I can see two sides of the 'Airbender' issue. For the most part, there are three groups in the debate:
a) Those who hated it because it ruined the show's good name.
b) Those who hated it because it was a terrible movie, regardless of being based off a TV show.
c) Those who liked it ? and probably were either asleep or on hallucinogens.
I fit squarely between Groups A and B. From a fan's perspective, 'Airbender' has ruined 'Avatar', which is world-renown for its beautiful imagery, believable characters, flowing plot, and incredible mythology. The movie captures none of this. While watching, I felt, in all honesty, as if Shamylan had skimmed through the Wikipedia page for the show and then decided to pen the script. The main characters don't even have their names pronounced correctly, which in any case is a complete disregard for or respect for the source material.
Now speaking as a film lover and from the perspective of a non-fan, 'Airbender' is still terrible. The plot?should you choose to call it that?is laughably condensed and incoherent. From the very start, I guarantee utter confusion. Why do Katara and Sokka (pronounced "sok-uh") help Aang (pronounced "ang") anyway? Why don't the Earthbenders even try to fight the Fire Nation? How did Aang get incased in ice? How could his master have been black if the entire series involved only East Asian-looking peoples? Shamylan felt as if he could fit an epic-in-scope, 22 episode long animé into 2 hours. He couldn't.
The cinematography is god-awful. Even without glasses this movie gave me the three D's: dark, dreary, and dull. The fight scenes look ridiculous?just people flailing like idiots. The series purposely avoided this by prescribing a different martial art to each element, but the film doesn't even try, and all we're left with is grown men looking like children in a McDonald's PlayPlace.
Speaking of characters, they are just plain bad. They have little to no clear motive, are in no way believable or likeable, and aren't true to the source, which by now is a redundant statement as none of this film is true to the source. Noah Ringer gives his most brilliant performance as the monotone, lifeless, cardboard cutout character of Aang. Except that Aang should be light-hearted, likeable, and an instant anchor-point for an audience that is unfamiliar with the world of 'Avatar'/'Airbender'. Katara comes across as a pinhead instead of a tough, smart young woman. Sokka comes off as genuinely unfunny and a jackass instead of genuinely funny and a jackass. Everyone else is wrong, too, I just don't have the energy to go into it all.
When I watched 'Avatar', I went in with as much of an optimistic mind as I possibly could. Granted, the idea that a source this rich and expansive could be condensed into a workable movie was a little absurd, but it's been done; 'Harry Potter' is perfect proof of that. Also, it was M. Night Shamylan. I couldn't just forget all the things he's done to me cinematically that just broke my heart, but then again, he made 'Sixth Sense' and 'Unbreakable', right? Surely this has potential, right? Wrong. I cannot find a single good thing to say about this movie. Try as I might, I've got nothing. Usually, I try very hard to give at least some credit to even the worst of movies and directors/writers, but 'Airbender' is impossible. Shamylan has lost all of his talent, I am now thoroughly convinced. Do not watch this movie, I implore you. It is, beyond a doubt, one of the worst films I've ever seen. Hollywood should be ashamed, Nickelodeon should be ashamed, and most of all, Shamylan should be ashamed. I would rather Michael Bay had made this movie. At least then we would've been given something visually pleasing with no 3-D option (because even Bay hates 3-D), which I've read is even worse than the 2-D version. If ever you are given the option between this and anything else, choose "anything else", because I'd put a Flying Bison on that "anything else" being more enjoyable.
P.S. The only reason I've given this a 10% is due to RT not allowing a 0%.