I saw the movie in both 2D (on a bit of a lark) and in 3D IMAX with my wife and 19 year old daughter. They were both surprised as how enjoyable the film was - but both thought is was too long by at least 30 minutes. (I did not feel that way, tho).
The story is basically 'Dances with Wolves' as I imagine it would have been (re)written by Isac Asimov (or Ray Bradbury) - so nothing really unique is going on with the plot. It's just been adapted for the alien aspect rather nicely, imo. The film is visually breath-taking, with no break in the action. I actually felt that I was part of the action in certain key points of the film. Very impressive.