I enjoyed reading my colleague Paul Watson's Avatar Review. See also the IMDB entry Avatar.
I too saw the movie and enjoyed it immensely, especially the full immersion in the 3D world that was so well realised. I too felt a bit let down by the black and white moral juxtaposition of the final third, that lacked all nuance. Would it not have been much more interesting if the military guys were real people too? or the if the plot had focused on another element of the rich world?
Strangely, as in no one else I have spoken to thought the same, I thought that the film was most like The Mission, essentially a recreation of the moral conflicts that arise with colonisation; for any American or European audience the main such example in our collective history was the discovery and exploitation of the "New World". Indeed the culture on the Avatar world does share many features of the native north American ethos. The Mission has a much more nuanced plot around the religious justification for joining the natives in resistance, and perhaps a more realistic ending where this resistance is doomed to failure against the might of European expansionism. I remember first hearing The Mission as a radio drama that dwelt even more on this debate, that was curtailed for the more visceral and visual movie. Avatar does include a sort of coming of age subplot that works quite well in terms of engaging the audience in the culture.
As for Paul's plea for a cinema that celebrates the science of exploration instead of the blockbuster military show down, perhaps I could direct him to the excellent Mars trilogy of books by Kim Stanley Robinson. If these are ever dramatised, they will need to preserve that focus to really reflect the books.
Also worth mentioning, for the most fully realised depiction of an alternative biology in science fiction is Brian W. Aldiss' Hellicona Trilogy Spring, Summer and Winter.
Despite its flaws, so well described by Paul, Avatar is one of the best science fiction movies of recent times. But really good science fiction is always better a book, as no director can ever capture what people can imagine in their own heads.