It was good, could've been better. Depite the story being stupidly overdone and cliché, this time it was done right, which I feel was a big advantage for this movie.
I would've loved some more "backstory" on the humans and earth, and know why it was so important for them to get this metal they wanted, and just have that in mind, so you could better understand all these actions they did. Because to me, the humans were just dickheads, without clear reasons for being so desperate and cruel towards the Na'vi.
Instead 80% of the focus was on how Sully and Neytiri fell in love, although it being a believeable love story, I would've liked to, as I sad, be more informed when stepping into this story.
And I think it could've been better as a book. But it was still a good, not brilliant, movie.