It's as far as I know the most expensive film ever, and in the ironies of life is one that preaches anti-violence with a war a main plot, and anti rampant capitalism, with a budget that could feed an entire country, but hollywood is not know for its congruency.
I has put computer animation to a whole different level, and the experience of seen it in an IMAX 3D cinema is just brilliant! The time passes flying and you don't feel it like a 3 hour film.
It's technically a great achivement, it almost felt like it was really filmed in Pandora and not just computer animated, it's truly a good hybrid between full live action, computer-generated characters and live enviroments, you can experience every breath of the fantastic creatures of the planet, and the movement of the plants, and the lights all around, and the sights of the planet are breath-taking.
As for the sci-fi, whilst is not hard core sci-fi, I think it made a very good work, there's no great violations of the laws of physic in it, well maybe the flying mountains, even when they could be feasible, but not very likely to happen. The space ships at the beginning are just great, they use Charles Pellegrino's concept of the Valkyrie which is sound science based.
Just a minor thing I didn't like, Pandora supposed to be a atmosphere satelite (moon) of a gas giant, who resembles Jupiter, like Titan on Saturn; and the background planet is always seen on the sky, which I think is not possible since in rotation, there has to be a point where you will not face the planet if observing from Pandora.
The plot even when can be seen as a futuristic dance with wolves or pocahontas one, is nice, since it makes direct critics to war-based states, and greedy wars (as the Iraq one) you can see it with quotes like:
"when someone is on top of something you want, you make them your enemy, then you take it from them"
"Our only security is in a preventive strike"
"We will fight terror with terror!"
"I was a warrior who dreamed he could bring peace, Sooner or later, I had to wake up."
Being against that kind of state behaviour myself, I like it very much.
The plot is centred on natural balance and the spiritual side of it, with a pantheistic or even neo-pagan flavour that give me a good taste of the movie itself. Even when Sigourney Weaver character says that "We're not talking about pagan voodoo but something that is real biologically: a global network of neurons." it really shows the concept of a web of life and a earth goddess in a fantastic way. The Na'vi had a connection beyond sentimental to the world around them, it's a real one. And many other pagan concepts as the Tree of Souls (Tree of life), the ancestor veneration, the life force that flows in everything and everyone; that we're all connected by some unseen and wonderful spirit, nature is sacred, and it's our duty as the created to care for the rest of creation. It was for me the ultimate pagan film.
Although it uses the typical concept of industrialized civilization vs primitive one, which I don't like, since I think that a balance can be achieved, it's plot really move me in some parts emotionally.
I really recommend it, I think is so far the best work of Cameron.