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I remember seeing the first ST movie at a theater with a friend (his mom took us, we were 12/13) and being wowed by presentation of the retrofitted docked Enterprise on the big screen. I put that moment right up there with the never-ending Imperial Star Destroyer at the beginning of the first Star Wars movie (IV).
I enjoyed seeing that Enterprise many times over on a giant screen on Disney's Great Movie Ride.
EDIT: Been enjoying the soundtrack themes to the ST movies...good stuff.
The first Trek film I saw in the theater was ST II. In fact, I didn't see TMP, ST III, IV or V until much later after release on VHS. I did however see ST VI and all of the Next Generation movies in the theater.
edit: Concerning the soundtracks, they are all indeed very memorable. Jerry Goldsmith's score for TMP is a classic and James Horner did a great job with both ST II and ST III.