I think the biology and the environmental message make Avatar the most important SF film since 2001: A Space Odyssey. The tree-root network is similar to a real root network of fungi that connects all forests around the Earth. Also, the sex-connection among diverse species reflects today's understanding of DNA transfer among species. The gender balance is also impressive. I can see how Cameron trimmed the original script so as to increase the impact of female characters; for instance, Neytiri concludes as a warrior/savior, not just a pregnant trophy as in the original. I hope the sequel will continue the environmental aim and develop the gender balance even more.