Low budget summer action movies are allowed to have a crappy story with lots of fluff, it is part of their appeal. This was not a low budget action movie.
Details of a movie or setting should be transparent to the audience. Being aware of them means the movie failed to draw you in. Now there are things like the floating islands that you can use to show the truly alien environment and that is ok (especially since they did it from a human's perspective).
Things like "Unobtainium" breaks one out of the immersion. Once immersion is broken it is hard to get back in.
I will say that as I've aged (and taken a few film classes [probably a bad idea]) I've demanded more out of the story of the film than the look of the film. At the same time I try to keep expectations inline with how the film is promoted. Like when I see a Nicolas Cage movie I don't expect a great film that has me thinking for days on end. But Avatar promoted itself as this epic movie and, IMO, it failed to live up to it.
