Spoilers below. Read at your own risk.
Please forgive any bad grammar and writing in this review: I'm extremely tired while writing this and there is so much to discuss.
My Grade - D. I could give the movie an F, but I think that would be too harsh. Transformers 2 deserves a F; this movie isn't that bad.
Quick summary: The movie needed another 45 minutes, better choreography, and to be written and directed by someone not M. Night Shyamalan.
Full review: Disappointing. Awful. Failure. Those were the words that spring to mind after seeing this movie. I was hoping for a grand epic, but all I got was trash. It was a horrible, horrible movie. In the interest of full disclosure, I have to say I am a huge fan of the show. IMO, if someone compiled a list of the top 10 or 20 shows created in the past decade, Avatar: The Last Airbender should be on that list. However, what makes the movie bad is not that it wasn't enough like the show; it's just that it was a bad movie. First, let's go into why it was a bad movie. Then I will go into how the movie could have been more like the show.
Directing: M. Night was just the wrong director and writer to pick for this kind of movie. This movie should have been staged as an epic fantasy with awesome martial arts action. It could be deep and spiritual (something Night tries to accomplish in his other movies), but it needs to be fun to watch and dazzle the eye. The movie doesn't do these things. There are too many close-ups, and weird shots, and horrible lighting. And the choreography suffered as a result.
Choreography: They really should have gone with a director who has more experience with this kind of thing, especially because the martial arts play a pretty big role in the universe. There were a couple of cool moments, but they were few and far between. The characters seemed to spend more time talking about action instead of allowing us to see it directly. And what action there was not impressive. When the action centered on Aang or Zuko it was okay, but otherwise, it was incomprehensible. I don't know how you can have two armies fighting and make it seem like nothing is happening. As a martial artist, I was disappointed in this, especially since the choreography in the show was top notch. Some of the action scenes could have been lifted frame by frame of the show, but they never occurred in the movie; like there wasn't enough time for it. This leads me to the next problem...
Writing: The movie needed to be over 2 hours, maybe 2.5 hours. Right now, it barely clocks in over 100 minutes. There is a reason most live-action fantasy movies are long; they need the time to establish the world itself, and the characters that make us care about the world. While I was watching the movie, I felt lost. At times I thought, 'Good thing I've seen the show, otherwise I wouldn't have any idea what was going on.' The movie jumped from place to place, seemingly at random, so it became difficult to know who I was looking at, where they were, and when they were (the movie takes place over several weeks, but there wasn't much of a sense of time.) And the dialog was horrible, with the characters having the amazing ability to state the obvious. There was no sense of humor or fun at all. There was only one intentional joke that got a laugh out of the audience. The dialog was laughed at more often than anything else. The characters were the worst victims of the writing. Sokka and Katara were barely in the movie, with the flimsiest of reasons given for why we should care. All the characters were similarly short changed, including Appa and Momo (that might have had more to do with budget constraints.)
Acting: I'm not going to go too much into this, because the actors had very little to work with. It was hard to get a sense of who the characters were, and how they should be acting.
Now, on to how the movie could have been more like the show, and how it would have been a better movie as a result. There was no chance the movie was going to be exactly like the show. I was willing to accept that many characters weren't going to appear and some events would be condensed, but the show just did everything better than the movie.
I'm going to nitpick first: WTF was up with the pronunciations. Characters names were pronounced differently than they were in the show, and there was no reason for it. Why say Aang differently in the movie than in the show? It just makes no sense. It has nothing to do with the quality of the movie, but it was an unnecessary change.
Another needless change: Firebenders now need a nearby source of fire to bend. They can't generate fire by themselves (unless under special conditions). Not really a huge change, but I'm scratching my head at why they made the change at all. The show managed to work it in and not have firebenders be overpowered.
Here is a prime example of where the movie should have taken something directly from the show: In the first episodes, Zuko captured Aang and holds him prisoner on his ship. Aang escapes, and in the process, Zuko's ship gets damaged. This forces Zuko to dock for repairs, which is where we meet Zhao. This was a logical way to have the characters interact, and gave us insight into their personalities. In the movie, Aang escapes from Zuko, but Zuko's ship is undamaged. While sailing after him, Zuko just happens to run into Zhao, who invites Zuko onto his ship for lunch, humiliates Zuko, and then Zuko leaves. That is how we are introduced to Zhao. It came across as awkward in the movie. I don't know why they didn't more closely adapt what they did in the show. It worked perfectly.
Another example: Ozai has a fairly large role in the movie. In the show, we don't even see his face until season three. The only reason this is an issue in the movie, is that Ozai didn't need to be there. We had two antagonists already, Zhao and Zuko. Every scene with Ozai ate up screen time for an already too-short movie. They should have spent more time developing the relationships of the other characters than dealing with Ozai. And don't get me started on the absence of Roku.
Some changes for the better: Sozin's Comet wasn't mentioned until the end of the movie, which worked out well. There was enough motivation presented to have Aang go to the North Pole without that plot thread being introduced. And the comet is three years away, not arriving by the end of the summer, which is what happened in the show. It was a smart change, considering a trilogy was planned and Night had to accommodate how the actors would age during production. Hopefully, the trilogy will not be made with Night as the director (if it's finished at all.)
I can write a dissertation on how the movie went wrong, but walk away with this. I'm not some fanboy who is upset the movie didn't do what the show did. It was just a bad movie, period. As a fan, I'm concerned by what this means for the franchise. Chances are, the trilogy won't be made because it will be damaged goods. I know Nickelodeon is working on a new Avatar mini-series with the original creators of the show, so there's that. I'm worried about what's going to happen after that. Nickelodeon might have forever tarnished one of their strongest franchises by putting it in the hands of M. Night Shyamalan. Hopefully his career will finally be over after this failure.
I'm looking forward to hearing other opinions; especially from people who have not seen the show. Maybe the movie isn't as much of a train wreck as I think it is.