I just bought the DVD of this movie. And rewatching it, yeah, it has some problems. I still say it has some of the best character moments in the series, especially among the "big three", AKA Kirk, Spock, and McCoy. It's kind of interesting watching the behind the scenes documentary, though, how Shatner seems to blame the fact that the movie kind of flopped mostly on the special effects. His point pretty much seems to be "If we'd had a decent rock monster, this would have been a great movie." Harve Bennett, on the other hand, seems to think that the whole premise of the movie seemed to be not that great. And though he never says as much, you can tell he's kind of embarrassed by this movie in a lot of ways.
Though there was a reason ILM didn't do the effects on this movie. At the time, they were swamped. That was the summer of all the big blockbuster sequels. They were working on Back To The Future Part II, and probably doing pre-production on Part III, they were doing Indiana Jones And The Last Crusade, they were doing Batman, and they had a regular chore doing work on Star Trek: The Next Generation. They just had a lot on their plate that year, and Star Trek V was obviously one more thing they didn't need.