My wife and I saw Avatar last night in 3D, and we both totally enjoyed it. Yes, the plot was somewhat simple, and yes, it is a white man's escape fantasy. (I mean, what people would let an outsider lead them into war after only 3 months?) But that doesn't take away from the fact that it is a very good movie, which my non-SF-loving wife loved as much as I did. That last fact speaks to why this film is so successful with audiences.
What really impressed me was that the science behind the movie was so accurate. No Star Trek red matter here. For anyone interested in the science behind the movie, go here. I should note that Cameron's comment about writing science fact instead of science fiction is arrogant and irritating, but in light of how accurate the science behind the film is, I'll give him a pass.