When you're watching it, don't compare it to the animated series and don't expect that much. That way, you can enjoy it. I give it a 7 and a half out of a possible 10.
I haven't seen all of it yet and I'm currently rewatching it but here's all I got so far. Some of them I got from what I've seen so far, some I got from Wikipedia, some from the trailers. I'll update this later once I finish the movie.
-The action scenes were pretty good. Even if the movie isn't all good, I'm sure you can enjoy the fight scenes.
-Awesome graphics. 'Nuff said.
-I like how they changed the Firebenders to control fire, not create it. Though it's sort of less epic.
-The background and the places were beautiful.
-The sounds and music was pretty good.
-I like some of the movie changes and additions.
-They cut out some stuff I didn't like in the series.
-The martial arts and Bending moves were great.
-Don't boo at me but...Yue was hot. ;)
-The acting was very bad. Although some, like Aang and Yue, were great, overall, the acting is very bad. Aang just needs more personality and experience. I'm sure that by the third movie, his acting will be better and maybe some of the others too.
-The name pronunciation. I know, it's minor. But it just bothers me. Although, it's sort of fine.
-Lack of humor. I get they're trying to aim it for an older audience but they should at least put effort in a bit more humor.
-They cut the Kyoshi Warriors, Roku, Koizilla, some good lines and scenes.
-Sometimes, some parts of the fight scenes look fake. I know they all are but some parts you can easily tell.
-The fights are too short. I expected a cooler battle with Zuko and Katara. Actually, the entire movie was too short.
-The movie goes too fast. Well, I guess that's what you get by turning a 10-hour season into a 1-hour movie. It would have been better if they made it 2-hours, so they could fit more stuff and the movie wouldn't be too rushed.
-There's too much slow-motion. It's supposed to be fast-paced with some slow-mo but they overdid it.
-Some characters are too out of character. Katara scared and weak? Sokka humorless? Aang...is just wrong.