The movie is worth seeing for the 3D and computer animation. The plot is what you would expect though, recycled from many other movies. It is Dances with Wolves meets Fern Gully. Also the characters are the only thing that don't make it into 3D. They all stick to their 1 dimensional motivations. After about 20 minutes into the movie you know how it will end and what each character will do.
All that aside though, I was in it for the visual effects and that didn't disappoint. See this movie in the theater. It will have very little to offer on DVD when it will be just another 2D alien action movie with a recycled plot.