I'm a bit new here, so what better way to share a little bit about myself than to describe a couple of my favorite theater experiences!

Fellowship of the Ring: I saw FotR on opening night in a big theater with about 500 people in it. It wasn't like the typical stadium seating multiplexes that are everywhere, it was more like a modern movie palace with only a few screens, but it was a pretty big theater with a really big screen and a steep slope to the floor so that pretty much everybody had a good view. The sound was cranked so high that the nazgul screams almost instantly gave me a headache, but I didn't really care. When the movie was finally done, I sat mesmerized for a little while after the credits had finished, letting it all sink in. My favorite book had made it to the big screen, and it was actually good.
Return of the King (trilogy screening): The first time I saw RotK was during the all day trilogy screening event that showed in a few places around the country when it premiered. I got to the theater at six in the morning and waited in the bitter cold with a bunch of other folks. A few people were dressed up in costumes, but most people were just in as many layers of coats and blankets that they could keep on. One group brought a horn that they played at intervals, counting down to the start of the first screening that I believe was at 1pm.
They finally let us inside the theater late in the morning, and everyone was chattering excitedly before the extended version of Fellowship started up. After the extended version of Two Towers finished (which had just recently been released on DVD, so a lot of the audience hadn't seen it yet), it was time to start Return of the King. I don't think I've ever been in a theater more excited and energetic that that night. Unfortunately for us, the projector had had too much fun during the day, and it burned through the film right in the middle of the Shelob sequence. They had to replace the projector and start the movie back up from the next reel. Subsequent viewings revealed that we only missed about a minute of the film, but that night we had no idea how much we had missed.
As soon as the spiffy end credits came up, there were a tons of cheers, and the individual cards for each cast member got a ton of applause (even Sean Bean got a lot of praise). Even though it was a *long* day at the theater, I'll never forget it. I've still got the keepsake they gave us at the end of the night.
The Matrix Reloaded (midnight): I went with a couple of my college buddies to the midnight showing of Matrix Reloaded, and it was a blast. There was a radio station there giving out prizes, and everyone was really pumped. The movie may not be the best thing in the world, but the experience that night was a lot of fun.
Scooby Doo: There's nothing like seeing Scooby Doo in a theater packed to the gills entirely with college students. I probably like the movie more than I should to this day, just because I saw it in the theater this way.