We don't really know anything yet, except that Avatar centers on a story of Earth exploiting a planet with an indigenous species on it. (the Prime Directive from Star Trek never looked so good now)
But honestly, what hasn't been done in sci-fi that Avatar won't borrow from?
Epic Quests?: Star Wars
Exploration: Star Trek
Alien Killers: Alien
Classic Sci-Fi: 2001
First Conact stories: Several
Conquering Aliens: Dozens
There's got to be some twists in this film...I can't think of what they'll do...
"All we have to decide is what to do with the time that is given to us."
Maybe aliens visit out planet to destroy us, we win, and those that are left on earth are put in concentration camps, the aliens revolt and ultimately prevail against us.