I saw Star Trek II in the theater. It wasn't opening day, but it was not long from that. The theater was packed by all sorts, and not just the fans. People laughed in all the right parts, and when Kirk was ambushed and later screamed "Khan" in anger, the theater was totally quiet afterward. Spock's death resulted in some people crying. You could hear them. When the movie was over, the theater erupted in applause.
My parents took me. Neither one was a Star Trek fan, but my mother remarked that it was a good movie and so much better than the boring first one, which she'd had to sit through for my birthday party. The next day in school, quite a few kids had seen it, and even among the non-fans, there was a general agreement that it was good. When I went to college a few years later, our dorm had a dozen or so movies on VHS, and TWOK was the only one that was constantly out. Its effect was everything they'd wanted for the first movie, even though this one was made and marketed more cheaply.
It's funny how I hear that the SFX aren't good -- to me, they hold up very well for 30 years. Is it that they are models instead of CGI? The latter looks like a videogame on steroids to me -- just overcomplicated animation that is rarely convincing. The style of flimmaking is different, of course. For the past ten years or so, most films have had a greenish-gray cast to them, as though they were all filmed on an overcast day in the American midwest. So, the actual film may look dated in this respect. But, to me, the movie holds up very well.