I haven't been this hyped for a movie since Watchmen came out.
As far as I can tell from the trailer, the film has earth millitary landing on a planet called Pandora, set on stripping it of a natural resource (some kind of rock). However to do that they need to get the native aliens (Na'vi) out of the way.
Rather than taking the resources by force, the plan is to put some of millitary personnel into a host Na'vi body (an Avatar) and negotiate with the natives.
I assume from that point the protagonist learns more about the natives eventually siding with them, over the earth millitary in a Dances with Wolves/ The Last Samurai style plot twist.