I thought Jim Cameron's Avatar was fantastic, and I highly recommend that if you're going to see it, that you see it in IMAX 3D if at all possible to heighten the experience.
As people have already stated in various reviews online, the visuals and CGI are exhilerating and fun, and that alone is worth the ticket price. The most notable achievement in this film is that the alien Na'vi characters, rendered completely inside a computer, looked believable and real. In the past, all CGI-generated people looked like beautiful but emotionless puppets, whose mouths and eyes did not accuately reflect realistically. Avatar finally got that down pat, and down right.