I thought there were some obvious cliches. Including being chockfull of "green = good, military and business = evil". Existing indigenous race taken advantage of by said evil business/military concerns.
Of course, there are no completely original stories in the world. Pocahontas stories, both real-life and instructional, have been retold for millenia, without a doubt. Good vs evil in whichever culture produces the stories will be told and retold.
However, the special effects were absolutely spectacular. The story was decently developed. Nothing really stupid or unexplainable happened (although remember - science fiction requires a certain amount of suspencion of disbelief - but good science fiction makes that easy by not being obviously idiotic). It showed reasonably well some things to be cautious about as man moves off his home world and starts to explore, possibly interacting with other cultures/intelligences (which is one fo the central themes of real science fiction, as opposed to most of "popular" science fiction seen on the screen). It makes a good use of science in many places, having done much better than most "science fiction" movies, which are usually really terror movies set in space instead of on Earth. The only real problem I have with the science in the movie (that I can remember) were the floating mountains. I can't really imagine anything natural, within the bounds of physics, that could account for that.
Spectacular movie. Anyone who says that it sucked really ought to make their reasons known, in my opinion.