My Take On Avatar
The biggest thing for Avatar, and it's a huge one, is that it brings Pandora and its inhabitants to life. The 3D part works very well (at least for my limited experience of 3D theaters), photography is awesome and chase/action sequences expertly crafted (as you expect from Cameron); the pace of the movie is not relentless but neither boring.
The various alien creatures and the Na'vis appear pretty much alive and real. Most plants and animals are, if not biologically correct, at least plausible.
The movie is a great, engrossing show, I can only recommend it under the entertainment aspect.
It is probably true that Cameron has set a new standard and made a movie like was never seen before.
But if you're looking for complex characters and a profund storyline... well, better search elsewhere. Acting is not bad but most characters are for them ost part bi-dimensional.
The story at its core is just another anti-colonial, anti-corporate scred. Noble savages who care about their environment (Na'vi) against humans intent on mining a very valuable mineral. Ah, and a totally badass Colonel.
There's a lot left unexplained, tho. Apparently Earth is a dying world, but humans are mining Pandora only out of greed: not even a mention of the uses of unobtanium.
Jake's change of sides just happens, there is very little exploration of his reasons for something so radical. Equally, it is difficult to believe that Neytiri would so easily go against the customs of her people and clan - and get so little opposition, too.
The whole plot seems contrived so that it can end with a massive final battle in which scores of humans will be slaughtered, the bad guy get his dues and afterwards the Na'vi will go back to their noble ways of respecting the environment and living peacefully.
The military aspects of the story are not handled too well, especially considering that the famous "nuke the entire site from orbit" comes from another Cameron movie. Sending all your forces out over unfamiliar terrain where electronic systems will be disrupted does not quite match the previous concept.