The movie was fantastic; amazing graphics, characters, storyline (although it was totally Space Pocohontas). However this game was not fantastic at all. The graphics are pretty good, but not that epic. The small part of one forest is in night time, and it does look pretty nice with all its florescent colours and what not. The ability to have it in 3D is nice too.
The gameplay itself lacked effort, and there were some plot holes too. For example, everyone spoke English? Another was that you were able to mount any Mountain Banshee, though in the movie they are meant to bond with a Na'Vi for life.
The game could have been so much better. It felt is though they had rushed it. They could have improved it by perhaps letting you customise your character's face and body, letting you persue romances, or at the very least have side quests. Instead of making the game based on a time before the movie, they might as well have made the game a remake of the movie itself. They could have spent more time on it then.
In my opinion this game was a let down. But it is something to keep you occupied if you were bored and had nothing better to play.