I loved this movie.
Btw, aren't movies like Batman and the Avengers unoriginal as well.. after all, they are based on comic books that have been around for half a century.. and no one calls them unoriginal. - With that said, both of those are also in my top 10.
Unoriginality isn't the only complaint that many people have against the movie. They also say that it has flat characters, thin plot, complete lack of depth, hammy dialogue, etc. I agree with some of these claims, but I still thought the movie was enjoyable, personally.
I actually thought that the two protagonists, Jake and Neytiri, were not flat (yet not fully rounded either - somewhere in between, if you ask me), and I actually felt that they had a likability (both in personality and in physical appearance) that made the movie entertaining. But I did feel that the villains were one dimensional. But still, I thought the characters were fairly effective, and the relationships between them were sufficiently established up to a point where I actually cared about them.