Avatar is Pocahontas set in Fern Gully, except with Smurfs who are Thundercats. And hero's plugged in from somewhere, with a smattering of a messiah complex thrown in (and a pity, they'll never make any sequels ... *ssh*).
But now that I've got the cliched bits out of the way, let me rave about the visual beauty of the movie. The reason this movie takes so much flak about the plot is that the CG does not jarr the suspension of disbelief required. To watch Neytri wail and definitely do the damsel in distress routine does bypass the fact that she's a giant cat-alien, into my emotional awareness. Somehow that disrupts the dehumanization of the enemies that the Colonel is under (if he had a cigar on him, I'd have had Quake3 flashbacks). The fight sequences are hardly overdone and they haven't gone bullet-time or john woo freeze-frames on it. Perhaps the brain-stem connections all animals share is probably the only thing that really stretches the imagination. But the movie goes to great lengths to illustrate that it's not really a form of direct control. There's hardly anything wrong with the movie as such - as long as you're only watching it.
There's EPIC FAIL and some glimmers of brilliance in the fauna of Pandora. Most of the animals on the planet have six limbs. This is perfectly acceptable, but if only they'd kept it consistent and extended it to the Na'avi. A bipedal/tetrapod Na'avi co-existing in parallel with hexapodal large animals sort of suggests a really un-bottlenecked evolutionary history (think of the Cambrian explosion, followed by millenia without an extinction event). Which would almost make the nerve fibre connections into a miraculous act of convergent evolution. But not all of it is bad. The lung openings on the direhorses, on their chests with a large volume intake, would've been a brilliant evolutionary jump away from a narrow trachea and probably an easier jump from book lungs & gills. Somehow the fauna is vaguely reminiscent of Nemo Ramjet's Snaiad universe. Last but not least, Turok - the flying giant in butterfly colours. I just can't get over the fact that its name is "last shadow" and the import of that.
All in all, it's a mish-mash of the noble savage, the greed of man (ah, Rousseau vs Hobbes), the modern industrial military complex and an imperfect romance. The movie is watchable, though not by any means an instant classic.
--If you want a happy ending, that depends, of course, on where you stop your story.
-- Orson Welles