I saw this last night in 3d and here are my thaughts: (Warning May Contain Spoilers)
The basic plot is predictable from the off, not only is it obvious from the second they unviel the Avatar bodies, but it is a story that has been told countless times before, Pocahontas, Last of the Mohichans, Dances with Wolves etc. The only difference with Avatar is that the setting has been made extra-terrestrial. Even though the formula of conqueror going native isnt a new one I still found the story very gripping and enjoyable and I found myself relating to the characters and finding them believable.
Now for Avatars real achievment, I can honestly say I've never seen anything so visually beautiful in my life. James Cameron and his creative team have really set a new benchmark in terms of visuals, from the complexity of Pandoras Flora, Fauna and wild life, to the stunning post sunset neon floorshow. It truely has to be seen to be believed.
The 3D version of the film really compounds the visual beauty, while every single thing is not sitting directly on your lap, every aspect gains a new depth and quasi-realism and you feel brought into the film by the little things, such as falling leaves which you do feel are only a few centimeters away
I commented to my friend as we left the cinema, that although I thought Avatar was one of the best films I had seen in a long time, I would probably never see it again, as the small screen and DVD would never be able to do the film justice