I saw this in 3D on Friday afternoon and loved every second of it. The story, while simple, is engaging and you find yourself really caring for the characters and their journey. It definitely adheres (at least in part) to Campbell's archetypal "hero's journey" structure, and I think that is going to be a large part of the film's success in word-of-mouth reviews.
Technically speaking, the animation on the Na'vi is very well done, and at times you forget that you're looking at CGI (or at least I did). The environments are absolutely stunning (even if they did remind me, on many occasions, of Felucia), and the 3D is never really used in a Johnny LaRue fashion; that being said, the sequence where Jake and the Banshee choose each other in the floating mountains could probably inspire some vertigo-like symptoms if you're not into heights.
But yeah, I enjoyed the film overall. Visually stunning, a good archetypally-based story, and good performances from the entire cast make this worth watching, IMHO. I'd rank it as my third favorite film of the year, behind "Up" and "District 9."