Having seen A Christmas Carol in 3D, I'd say that 3D is a waste of time and snacks. I saw Avatar, and it's not worth seeing in 3D, however, it is definately worth seeing.
The writers and special effects team worked their asses off for this film. The graphics were beautiful and the concept of Pandora was innovating. The story is slightly overused, but then again what isn't these days. However, this version of the story might actually get non-eco-friendly people to wake up and smell the industry. The acting from Zoe Saldana is Oscar-worthy, and I liked the wheelchair-guy, too. It's a great movie, worth-seeing, just try not to get naucious while watching the 3D version.