9.5 out of 10
Acting could have been better, not to say it was bad or even not good, it just could have been considerably better. Especially Sam Worthington's performance, it left some more to be desired. Also, the cast wasn't what I would call a great or particularly memorable cast. Average, maybe somewhat good at best.
The parts with the Na'vi and in the forests of Pandora were the parts that stuck in my mind the most, and were in my opinion the best parts of the entire movie.
Also the movie left some elements unexplained. Things that, in my mind, would have really helped the story. If you watch or have already watched the movie you will probably find these same exact parts too, and you'll know when you say/said "wait, what?" to yourself.
No, it's not a perfect movie, but at the same time, it's not even close to being bad or even mediocre. In the very least it's one of the best pieces of film making that has come out in the last several years. A must watch in my opinion, truly more of an experience than a movie and more of an event than a viewing.