I was 20 years old on saw it open night with my girlfriend and our usual group of friends. Most of whom were long time Trek fans. I recall clapping when Gene and the actor's names came on screen. Also when each character appeared on screen. We loved the new looks for the Klingons and the Enterprise.
My friend got the idea to use TMP set a record for the number of times watching a film. So I wound up seeing it way too many times. The flaws really begin to jump out when you do that.