Alas most-popular and biggest grossing don't always equate to "Best".
I have not seen all of 'Avatar'- mostly 'tube' clips, but it would have to have some REAL depth to compare to Hurt Locker or Up In The Air, both of which I have seen. From what I
have seen (SFX aside) its just a tad too 'right-on' and Eco-Correct.
Avatar & Star Wars are both good examples of where Sci-fi falls down.
While most films rely on cliches and cultural morres but try to work around them, a good deal of post Star Wars sci-fi tends to positively embrace them and comes across as rather lame.
Where films like TDTESS, Failsafe, Them, and Star Trek OS (betraying my age here) trod 'new' ground in terms of exposing a mainstream audience, albeit metaphorically, to non-mainstream social commentary and ideas, SWs and Avatar both seem to parrot their contemporary zeitgeist & convention.
Thats not to say I'm not going to rent a massive projector and watch 'Avatar' against the shed wall- it looks breathtaking!!!!

Just not thought-provoking.