Watched it yesterday in 3D. In short, I think it is a triumph of style over substance.
The general idea of this movie is an exact copy of The Last Samurai, which in turn is an exact copy of Dances With Wolves, which is probably an exact copy of some other movie I don't know about. Do I accuse Avatar on this basis? - No. For me, it fails in a different department. I didn't like how the story was portrayed. Not that it was bad - it was quite good - but it was nothing original. I expected originality from such an advanced movie. To illustrate what I mean, I will compare it to another recent movie: District 9 (D9 for short). D9 also has a cliche idea it its core: being rejected based on prejudice and bias, etc etc. That idea has been convayed a thousand times before, just like Avatar's idea. But what D9 achieved is originality in story-telling: first it was more of a documentary, then it becomes a drama/thriller and finally, an action movie.
To expand my point about Avatar's lack of originality, I will continue comparing it to D9; let us move to the character department. In both D9 and Ava, you have a sci-fi/fairy-tale setup for the action. Yet, Ava is too afraid to make the leading character anything original; it's the same action hero we've seen a thousand - no - a million times before. In D9, however, the hero is a kind-hearted, a bit of a douche, spiritually weak man whose weakness makes him follow the bandwaggon of hating the prawns just because they're different and kid of 'oppose' society (when in fact, they're like that simply because society rejected them and doomed them to a life in the slums). I find Wikus much more interesting as a character than Jake, simply because it is something you don't see as often.
Acting was nothing good. Especially the princess. In D9, Sharlto Copley was very convincing; and he's not a big star with loads of experience, too. I applaud him.
Moving onto the script. I will not go into debates about the possibility of floating mountains and super-conductors. Most of the explanation is solid. The dialogue, however, was awful. D9 was better (not 'good', but not bad). You can make a blockbuster without cheeeeeesssssy lines. Why didn't Cameron do it? I think he was jsut too afraid to spoil his own fairy-tale of a movie. Also: why couldn't they drop the explosives from a higher orbit again?
If you're making a two and a half hour movie, you better fill it up with real content, otherwise it will get too boring for those of us who think that Transporter was bad. Did I care about the characters? - A bit. In D9, I really cared about the characters. Was Avatar entertaining? Yes. Did it reach its full potential - not even by a thousand miles.
None.