I say experience because that's what it feels like to me. More like a full experience than just 'watching a movie'. You really have to see it in 3D to get the full effect. You'll want to live on the alien planet by the end of the movie. I've seen it three times now and each time I see it, I don't want it to end!
I think the 3D was much clearer in the regular theater than the IMAX. IMAX made some scenes fuzzy. Not worth the extra cash.