I've seen all sorts of critical comments about the politics of these two films and while many of those comments may have some validity, I think both were great in many ways and definitely very entertaining -- an important consideration not always taken into account by reviewers!
Avatar was great because the good guys and the Earth Mother won, the evil corporations were defeated, and it was a very transparent criticism of the real-life way that corporations destroy the environment and indigenous cultures.
One criticism I read was that, by making the main human character (Jake Sully) the saviour of the indigenous people, it reinforces the notion that the "noble savages" need the white saviours, in the end. There may be an element of that, but I thought Sully's evolution from an economic conscript to rebel leader actually was a plot device to bring the audience from the mentality of the conquerors over to the other side.
Not that we, the audience, needed much encouragement. The Na'vi indigenous peoples were so clearly cooler and nicer than the cartoon supervillains who ran the invaders' mining operation. Another criticism could be that the characters were so superficial, and that the Na'vi rarely did anything to transcend the old "noble savage" archetype. Fair enough. But it wasn't a character-driven movie, it was an action movie with a couple of very political themes. And some brilliant scenery!
The Na'vi were kind of like a cooler, more sophisticated version of the Ewoks in Return of the Jedi. Actually, the Ewoks were a lot more fun, but it may not have been possible to sustain a whole movie based on them. Nevertheless the overall feel of the film was similar to Star Wars (but once again, much better politics).
The Earth-mother worship and the extreme "otherness" of the Na'vi (they are symbiotically and empathically linked with other species) was probably unnecessary. They are just a bit too cool for their own good, really. But that's not a major detraction. The film was great fun, slightly predictable, but for any fans of space opera and fantasy-action movies a must watch. Especially in 3-D.
But the next movie I watched, District 9, remedied many of the weaknesses of Avatar. The aliens were not noble savages, they were dirty and disshevelled refugees who have drug addictions (cat food!) and trade their weapons for it with the local (Nigerian) mafia.
A criticism of this movie was that the Nigerian thugs were the personification of all that old Apartheid South Africa thought of black Africans: brutal, stupid, thugs. This criticism is way off mark. The Nigerians' actions were a direct parallel of the other gang of thugs -- the MNU corporation. Their portrayal only highlights the crude evil of the Mengele-like MNU scientists and weapons researchers.
Meanwhile, the journey of the main character, Wikus van de Merwe, provides a lot of laughs. The aliens are not focused on as characters very much, the incredibly brutal racism of the MNU officials and the mercenaries is the real focus. And the hypocrisy and cowardice of van de Merwe as he evolves through the film. The semi-documentary style as van de Merwe cheerfully evicts aliens is a grotesque and horrific as it is a vicious satire on bureaucratic brutalising of vulnerable people.
Politically, I think it's not really a film about racism and apartheid (although the South African setting might cause you to think of that). I think it's more about the brutal way that modern governments deal with refugees and foreign populations in trouble. Think of Haiti now with US troops invading and spreading propaganda stories about voodoo-practicing savages who riot and burn rather than rebuilding.
The racism in the film is vivid and definitely lifted from the apartheid template, but the circumstances of the alien refugees are more a parallel with modern boat people than blacks under Apartheid. The bad guys are more believable than in Avatar, although the brutal, unashamed racism of the mercenaries in particular may be unfamiliar to many (but I doubt it's really that unrealistic).
Of course the film is an action extravaganza like Avatar, albeit with lots more splatter and vomit. It gets a bit predictable, and it's not all that deep, but it's a lot of fun. It was a blast.
Two films that were definitely worth seeing!