While the movie was visually striking, there are serious holes in the plot.
The story takes place 140 years in the future, and man has figured a way to create these huge beings by combining the DNA of both species, and then transfer the consciousness of a human into this being. Pretty heady stuff. At the same time, man has not come up with a less intrusive way to mine "unobtainium" than via scorched earth? We have to level this forest and displace all these different species to get to this mineral? C'mon, man!!
And this does not even get into the problems of this being a blatant rip off of 1992's FernGully: The Last Rainforest. (Watch the trailer on IMDB after you see Avatar.) Or Dances With Wolves, or Pochahantas.