In short it's about a guy who uses a sort of bio-engineered astral projection to occupy the body of an alien. He's a former marine, and the thinking is that if he can understand how the "natives" think on this nearby planet, he can talk them into moving out of the way while humans strip mine their homeworld for minerals. He can't, and becomes convinced by their side of the argument.
It's a stupid film. Disregarding the fact that the "powers that be" really should have spotted the psychological effects of allowing a disabled vet to be projected into something that walks, it's a film we've all seen 100x, if not 1000x before.
In addition it irritated me because it suggests Americans have learned nothing from Iraq and Afghanistan. Haven't we seen from those countries that Earthlings don't get booted out by "set piece battles." They're booted out by terror campaigns, and yet we're expected to believe that it's "set piece battles" that did for humans.
In addition, the ending was far too syrupy. If there'd been any more sugar in the script, I swear that I'd have come down with diabetes.
Finally, it's a 3-D film, and I found the effects beyond irritating. The film is long, too long in fact, and I wanted to scream because of the number of times we found ourselves looking at the protagonists through bushes, trees, the leg of animals, and over furniture. In short the effects got in the way of the film, to my mind, and needed to be pruned.
I can't think of a time when I hated a film as much ad this one. When I say I hated it, I really, really, really hated it beyond all imaginable description.