Some people like to go against the flow. They dislike things just on the sheer fact that too many people like the same thing. They would rather hunt for flaws so they can say they don't like something that majority of the population seems to like. Why do they do it? Well, what if I said...I personally didn't like all the Godfathers, Shawshank Redemption, all 3 Lord of the Rings. They were all are predictable and kinda slow. Hey, look at me! I have a different opinion! Did I get your attention? I was kidding about that, but I bet it kinda lit some kind of an urge to argue against me.
I 100% agree that Avatar is a rehash of a classic story like Pocahontas, but its told in a fresh new way. I never watched Pocahontas thinking, wow, I wish I lived in that Chinese village with all those talking animals. I never felt immersed in any movie like I did with Avatar.
If you expect the movie to do something predictable, you are just watching the clock until your expectations are met while totally missing all the good parts in the process. Why not do the opposite and hunt for something to appreciate. With this movie, its not too hard.