Dude, there is a sentient planet, which can be a euphemism for a deity. Every organism can "link" with each other, which has parallels with spiritualism and certain religions. And there were floating islands in the first movie. Floating islands. Thats the kind of shit you see in straight up Final Fantasy, World of Warcraft, Zelda, etc. The first thing to have floating islands was a fantasy book called Gulliver's Travels, and then it was heavily popularized by fantasy Japanese media. There are fewer instances of floating islands in Sci Fi media (floating cities don't count). So I'd say Avatar being more science fantasy than science fiction is accurate.