I saw it in IMAX 3D at AMC theaters and enjoyed it along with my wife. The story is nothing to write about but the technical aspects were fantastic. Pandora, the alien planet, was really colorful and the 3D effects seemed to do justice to the imagination. It seems unbelievable how realistic animation has really become. The pace was tight and engaging.
I would recommend watching the movie in 3D for the digital effects and wonderful use of the screen. Not sure whether one will get the same WOW factor in 2D.