I have seen this twice in 3D. I generally am ambivalent about 3D films, but I think this one makes reasonable use of the current state of the technology.
Briefly, I think this film rocks. It's formulaic and predictable, and somewhat heavy-handed in its message, but it's beautifully done and enthralling. I've found it very easy to suspend disbelief (though that's usually not a problem for me anyway).
Personally, I think _Avatar_ is to the current state of the film industry what _Star Wars_ was when _it_ was released: a groundbreaking phenomenon. And it's good, and fun!