I love this movie.
Whilst the execution of the Sybok plot didn't quite work, the concept was appealing and I thought the actor did a great job.
I LOVED the Kirk/Spock/McCoy scenes. For all people bang on about the friendship between them in the series, I feel THIS movie was the friendship at its best. Star Trek III perhaps demonstrated the loyalty more, but Nimoy was absent (onscreen) for most of it. Here, I just thought it was great. Especially when Spock and McCoy side with Kirk against Sybok.
The budget makes the film look cheap in places, but I like the tone of it - it doesn't take itself too seriously (come on, Trek fans - can't we have some fun once in a while!?), clips along at a fair old pace, and has plenty of action/adventure moments in it.
Yep, like somebody says above, I recognise the flaws - but it's still in my top 5 Trek movies to rewatch!!