I saw the movie Avatar last evening, the last night it was available at the closest discount movie complex (not in 3D). I was impressed! They got their $280M money's worth (and earned over $2.8 billion). The computer generated aliens and the world they lived in pushed the standard for those kinds of characters and images. The world, in the best traditions of science fiction, was well thought out with the implications for various features logically exploited. The movie didn't spoon feed or data dump explanations of how the world worked but merely showed how people expected to act in that environment and assumed the audience would figure it out. All of that in service of (and not overshadow) a rollicking good story. Well done!
As many others have noted the basic outline of the plot is not new. Dances with Wolves told a similar story maybe 20 years ago. This is not a problem -- most romantic comedies follow the same plot outline.
However, like many reviewers, I give it an A-, not an A. The gung-ho military and corporate people in this movie treat the aliens in the same manner those of European descent treated Native Americans. One can get tired of this and wonder why we didn't learn anything from our national history. Considering how gays are treated -- we're subhuman -- it is obvious we didn't learn that lesson. We've just changed the target. In addition, there are some sequences that show a lot of military violence (which go on too long). We haven't learned anything on that front either.