Ok right up front I will admit I am a ATLAB fanboy. Watched all three seasons first run and still watch it all the time. So I of course had big expectations for the movie, so where to begin...
First someone should take MNS word processor away from him right now because he can't write worth a darn. The movie races from begining till end with no character development. Example, watch an episode of the animated series and you will see how integral Katara and Sokka are to the plot, in the movie they have next to no screen time (in all honesty hardly anyone does). Next major torpedo in the movie is the editing, sloppy and uneven it jerks the viewer around leaving your head spinning. It has been suggested that the acting is bad and while they might not be "greats" of the cinema, the writing and editing did not do them any favors.
Now for the fanboy complaints. Appa and Momo, such fantastic creatures in the Animated series were side attractions, obvious slaves to the special effects budget they are ushered on and off screen as quickly as possible. Loveable Appa looks simply aweful, playful Momo just flits around. The pronunciation of names, ok for three seasons the names were pronounced one way but were altered for the movie. Everytime a name was spoken not as it was in the series it yanked me out of the movie. Such a bad decision, I really have to question MNS judgement here. Next is the element bending. In the series the element bending forms are elegant, directly broadcasting and in concert with the "bending" that occurs, in the movie every character adds a bunch of extra flourishes that make them seem like they are warming up before each move. Next in the series Firebenders summon fire directly from their Chi, they do not need fire to make fire as they do in the movie, it feels silly and while MNS said he did it to make firebending like the other bending, it came across to me as another budget saving move as they didn't have to pay for more CGI.Oh and add to the budget issues, the spirit world, what a joke.
There are tiny glimpses of what this movie could of been. The Scenes as Aang remembers the other Airbenders (which should of been part of the lead in to the movie, not the end!!!), A moment when Katara looks so much like her animated counterpart, Iroh showing reverence for the spirits.
If this movie somehow makes enough to warrent a sequel, lets pray MNS is kept far, far away from the project.