Most people who know about the Star Trek films feel that the fifth outing was the weakest of the series... and they're probably right. Nothing really fits for the big-screen. The villain isn't particularly villainous. The Klingon sub-plot is pretty lame. There isn't much action and there's never much of a feel of threat to the characters.
However, despite all that, the film isn't too bad. I look at as more as an extended episode of the TV show. The Enterprise gets taken over (rather easily in my opinion - it must have been the Security staffs' lunch hour or something) by some blokes wearing rags, lead by Spock's half brother (who should have been played by Sean Connery, only he turned the part down). Then, the ship is taken to the centre of the universe (which is apparently only a few hours journey away) in an attempt to meet God.
Since Star Trek 4: The Voyage Home had a lot of humour in it, it seems like they've tried to recreate a humorous atmosphere in number 5, too. However, it doesn't really work and take away what little tension there is for the situation. The banter between the Kirk-Spock-McCoy triangle is nice, but, again, it only serves to make this a light-hearted film that deals with serious subject matter.
William Shatner, aka Captain Kirk, also directs. And, to be fair, he doesn't do a bad job. Everything here is pretty standard stuff. It certainly won't win over many new fans to either the genre or the franchise. However, if you're a fan of the old crew and have an hour and a half to spare, there are worse sci-fi outings out there.