Second time seeing it, first time on IMAX (saw RealD before) - IMAX is worth it because of the sound system alone! Made the experience even more powerful. I didn't see a great deal of difference visually between IMAX and RealD, but the size of the screen was impressive. A great movie, technically brilliant, and Cameron has created a rich, stunning world that is as impressive (if not more so) than anything that has gone before (Lucas, I'm looking at you!) I'm ready to see it again!