My wife and I saw the IMAX 3D version at the SF Sony Metreon lastnight. She was very impressed with the 3D visuals (her favorite were the flying "jellyfish") and since I only have one good eye, I can't see in 3D (looks like a regular 2D screen to me), however, we both thoroughly enjoyed the cinematic experience.
As it has already been mentioned in this thread, the CG may not have been "groundbreaking", just more of it. But what really impressed me was the attention to the little details, i.e. blood, sweat, tears, paint textures on the Navi skin. That, I believe I have not seen (or at least noticed) before in prior CG movies.
BTW, we probably enjoyed Avatar a little more than usual because we spent Christmas in Yosemite's winter wonderland. Hiking around Mariposa Grove, Vernal Falls, Nevada Falls, etc.