It reflects on a lot of earth history and human morality. And it is also a very beautiful movie.
One of my favorite movies, and the extended edition makes it even better. The extended edition adds a lot of extra character development for Jake and Grace, which I think helped the story a LOT, even though I think the original was amazing as it was. While the story at its base level is nothing new per se, it's the execution of that story that makes it so memorable and moving. I think I may still watch the theatrical version on some rewatches for a couple reasons though: The extended version doesn't come in 3D (at least, not yet) and this movie is probably the best 3D movie in existence, and also due to the length. However if a 3D Blu-ray of the extended edition comes out I will probably end up preferring that one. But if you like Avatar and haven't seen the extended version, I HIGHLY recommend it.
The plot is rather dull, and naming the MacGuffin of your movie "Unobtainium" is a huge lack of creativity (and just too far of a suspension of disbelief).
James Cameron has always been renowned for his remarkable visual effects (and this hasn't changed with Avatar), but his movies used to have so much more than that.