This is about what happens when dudes with assault rifles and power armor attempt to take over a planet full of hostile flora and fauna. Without getting into heavy spoilers, the movie itself is a classic love story wrapped in a sci-fi wrapper. Film Jon Landau (who also produced Cameron's previous major movie, Titanic), commented, "if Titantic was a repackaged Romeo & Juliet, then you could say that Avatar is very reminiscent of Pocahontas. The movie is about paralyzed Marine Jake Sully who joins a mining company that is grabbing "unobtainium" from the planet Pandora. Since humans can't breathe Pandoran air, the scientists have created these weird genetic hybrids of humans and Na'Vi (the indigenous sentient species on the planet) that are controlled remotely (these hybrids are the "avatar" in question).
So the Pocahontas connection comes in when Jake is controlling his avatar to mine the planet, and meets a female Na'Vi that he falls in love with. And the game takes place before all of that, so if you buy it in the fall, you won't be spoiling the movie's ending for yourself.