IMO it wouldn't be worth it in 2D. The major selling point for me was the immersive 3D. This new 3D technology is pretty kickass, IMO. It's not like the old-school 3D where all they could do was throw stuff at your face. It's really quite a lot like being there. I want to see it again in an IMAX theater.
Having said that, the story was only so-so to me. It seemed like a mish-mash of Ferngully, Dances with Wolves, Pocahontas, etc etc etc. Very "noble savage." Joins a long line of "white guy who encounters a group of tribal people and becomes the most awesome one of them ever" movies.
ohnotheydidnt: Avatar: The Last Samurai of the Ferngully Who Dances with Wolves (And Why It's All Kinda Racist)