To be brief, it is brilliant filmmaking. Its action is coherent and exhilaratingly staged in an era where Le Cinema Du Blockbustré thrives on incoherence and meaningless stimulation. Cameron takes his time in setting up and telling his story, with each set piece coming out of that story instead of being shoehorned into it. Its computer-generated creations are not there simply to impress us, but to move us; its use of 3-D, that gimmickiest of gimmicks, is not gimmicky at all but, dare I say, artistic. It does not throw a bunch of shit at us, taking us out of the film, but rather gives the image layers of depth, bringing us deeper into it.
Glenn Kenny, in his review for the Auteurs, likened it to the work of Jack Kirby:
What I really love about Cameron’s sci-fi work is that it baldly reveals that one of his key visual influences is comics pioneer Jack Kirby, he of the galactic concepts, massive double-truck panoramas, and the craziest kineticism that was ever contained within none-moving frames, that is, comic book panels. Watching the camera pans going over the desolate planet landscape filling up with defense machinery in Aliens was like looking at a trademark Kirby two-page post splash vision come to life. It wasn’t just the composition and the larger than life humans; it was the hypertrophied design of the weapons and the air, land, and sometimes sea craft. A crazy, violent universe...[Avatar] works best as an insanely expanded Kirby-esque cinematic spectacle.
And this is a case where I agree with Glenn; I totally see (and definitely dig) the Kirby influence. The weird shapes of the flora and the fauna, the sometimes impractical craziness of, say, a trial of manhood that involves first jumping from one flying mountain to the root hanging precariously from another and shimmying up said root. I've written before about how Kirby often finds the sublime in the ridiculous, and Cameron does this in Avatar, tossing more ideas on the screen than most action directors have in their entire oeuvres. It's two-and-a-half hours jam-packed with exhilarating ideas, ideas that come together with a vengeance in the film's final act, especially with the introduction of a most unusual cavalry.
If someone tells you that the film devolves into mindless action in its last hour, they are wrong. If someone says the film has no ideas, no center, no originality, don't listen to them. Rather, feel sorry for those who have closed themselves off to spectacle, who can't appreciate or enjoy bombast at its most gorgeous and astonishing-- those people have cast off an entire and perfectly valid tradition of cinema, becoming like certain academics who can only celebrate the messy and the obscure, who are afraid to embrace something "popular" because it makes them seem less refined.
As for the putative political content, which caused quite a stir at Kenny's site a week or so back, I got to say that I don't think the film should be approached as an allegory for the most recent war in Iraq; while many of the men working for the assuredly Evil Corporation are former marines, they're no more members of the United States Armed Forces than the colonial marines in Cameron's Aliens. (And it's not like the Iraq War was waged for oil. No, no matter what your friend's protest sign says, that wasn't actually the case.) A better analogue for the Na'vi, if you must have one, would be the American Indians; the film is somewhat like Inglourious Basterds in that it provides a new (better?) ending to the whole sad saga: cinema trumping history.
But even that is a bad fit, in that, again, it's not a government but a private company that's waging this war for profit, not American soldiers but mercenaries. (Which does bring to mind the atrocities of that hated Octopus, Chiquita Brands International, nee the United Fruit Company...)