"I don't deserve their praise." No, you don't.
First of all, let me say this: Avatar The Last Airbender is one of my favorite cartoons of all time, and one of my favorite shows in general. I was quite excited about the movie.
Then I actually watched it.
The movie consists of five notable elements: the visuals, the effects, the writing, the actors, and the story. The general consensus is this:
Story: Bad, but gets some slack for having to summarize ten hours into 90 minutes.
While I mostly agree with one through four, I have to say they shouldn't even get the bonus points on story. After all, just look at Season One. Only a few episodes are absolutely essential to the story, and even less to the plot of the season.
-The two-part pilot
-The Blue Spirit
-The three episode finale
All Shymalan had to do was summarize these six episodes, and everything else was fair game. And don't forget episodes are 30 minutes with commercials. Without this, it's closer to 22 minutes. M Night Shymalan had to summarize two and a half hours into one and a half. Hardly a herculean task. If done correctrly, this movie would have spent 20 minutes on the pilot, then a 40 minute second act, and finally a 30 minute finale. The movie's structure is way off, and even if the acting was competent, the movie would still suck as a result. The failure of this movie lies squarely on the shoulders on the writer, M Night Shymalan. If they do make a movie of book 2 (which is far more story-driven then book one, by the way,) then a change in writer and core cast (well, I gues Dev Patel as Zuko was fine) is necessary for me to even consider spending money on it, and you should do the same.
And honestly? Why not go with a two and a half hour movie. That's what I was expecting, and it's been done before, to epic effect.