"Cameron said his inspiration was "every single science fiction book I read as a kid", and that he was particularly striving to update the style of Edgar Rice Burroughs's John Carter series. The director has acknowledged that Avatar shares themes with the films At Play in the Fields of the Lord, The Emerald Forest, and Princess Mononoke, which feature clashes between cultures and civilizations, and with Dances With Wolves, where a battered soldier finds himself drawn to the culture he was initially fighting against."
No it isn't the most original story, but it is told in an exceptionally effective and spectacular way. Cameron did Aliens and Terminator 2; I'm quite confident in his ability to make decent sequels.