I haven't said anything about Avatar until now because pretty much everything has been said. However, ten weeks into its run, I can say a few things.
The story of Avatar isn't all that good. Hardly innovating, it's Last of the Mohicans in space. It's the Great White Hunter sent to woo the natives but ends up going native (so that's where the phrase comes from).
Pandora is a moon, not a planet. It's a goodly-sized moon and it orbits a gas giant, but it's a moon nonetheless. The flora and fauna are iridescent because the planet is in darkness at least 5/8ths of the time, including long stretches of total darkness when it is eclipsed behind the planet.
The mineral, unobtainium, is a joke among science fiction writers going back generations. If it's not important what the mineral does, then giving it a perfectly descriptive nonsensical name saves pages of exposition, hence, unobtainium (it's rare, it's hard to find, it might be radiatctive! Unobtainium! On sale now!)
The Na'vi won the battle with arrows, rocks and large cajones. They didn't win the war. When the humans go back to earth, do you think they are going to stay there? No. They will make bigger, badder weapons, come back and annihilate the natives. The Na'vi are extinct but don't know it yet. For me, it was a sad ending.