It's THE landmark film for 3D, and for good-reason; the 3D effect, cinematography, and visual-effects quality, are just absolutely superb. That is the exact kind of 3D I'd want in my home, that I want directors to focus on - not the shitty, in-your-face, post-processing job, but truly filmed in 3D and not in a way that is focusing on gimmicks but rather Depth of Field and immersion into the scene. That is what I loved about Avatar.
The movie itself was completely "Meh", but the 3D was awesome.
I refuse to ever watch Avatar in 2D. It's not a movie I really care to watch, but it is a fun experience in 3D. Because that level of 3D is just that, an experience.
I am looking forward for the movies that will be using the same type of camera system used in Avatar, which include: the new Resident Evil, Tron: Legacy, Transformers 3, and in a few years Cameron will return with Battle Angel.