A spectacular film. The fact that the plot is somewhat predictable does not detract from an extraordinarily enjoyable movie. The lushly rendered alien landscapes leap off the screen in the 3D version of Avatar, and I highly recommend the 3D production. (I can't comment on the 2D or IMAX 3D versions.)
One suggestion: find a theater with comfortable chairs. With a running time of 2:40, once you add the trailers, you'll be sitting for close to three hours.