I watched it yesterday (Belgium is one of the first countries to screen the movie, weird). Saw it in 3D as well, which really adds to the experience.
The storyline is very predictable and unoriginal, the characters are zero, the symbolism is cheesy and the dialogues suck. However, for a movie of almost 3 hours I enjoyed it a lot and never got bored. It has great music, brilliant action, hot alien chicks and awesome 3D animation. This is the movie the 3D-cinemas have been waiting for and it is also the movie which places 3D-animated expressions and emotions on the same level as those of human actors.
He could have made it a lot better and deeper, I guess he had to make some hollywoodian sacrifices to keep it financable.
The stuttery trailers don't do the visuals justice, in the cinema it's pretty wonderful. The world is filled with huge luminescent plants, weird animals and stunning vistas.
If you are looking for a quiet, smart sci-fi movie: rent Moon and watch it at home. If you want to be really immersed in a beautiful, realistic alien world and culture and have some decent action on the way, Avatar is your movie. You'll walk out of the theatre hoping to meet a 3 metre tall alien with a bow around the corner.
Oh, if you can: do this movie on acid. In 3D. It'll blow your eyes out.