Surprised nobody's mentioned this on these boards yet.
I just saw it. I thought it was very good, but probably not quite the masterpiece that James Cameron had originally hoped for.
The visuals are the best yet seen, but they're still CGI, something we've had for over 15 years now, and the rendering (particularly of the creatures that inhabit Pandora) still has that plastic feel. The 3D worked well, but became less noticable as the film went on.
The plot itself (a bit like Fern Gully) wasn't especially original, though some of its mechanics were rather ingenious. The whole concept of an avatar, a being that one inhabits in sleep, was particularly intriguing and imaginative. As were some of the biological 'Gaia' type theories expounded by Sigourney Weaver, though they could have explored these in more depth. Also the way in which the main character's stupendous avatar incarnation contrasted so sharply his drab crippled human self had a certain pathos to it that could have been far more moving than all the eco stuff had it been developed further.
Characters were ok, but I thought the General guy was the most memorable, and a very good villain.
Overall I guess it was the predictable plot that let the film down the most. It was difficult to have sympathy for the Na'vi because as characters they felt a bit like every other representaion of threatend indigenous folk that we've seen in so many other films, their human counterparts felt a bit more real somehow, but perhaps this was deliberate. Ultimately it was still a very good film.
I give it 4/5.