The best experience I ever had with a movie crowd experience was my second viewing of THE BLAIR WITCH PROJECT. My brother and I went to see it on Saturday morning, opening weekend. The place was sold out, but it was a meh experience.
I had tickets for Monday night with a bunch of other friends, though, and that crowd was nuts. People were screaming at all the best bits and just really getting into the atmosphere of the whole thing. I would think people who didn't see it that way will never really grasp it's emotional impact.