I'm trying to think of good fourth installments and none spring to mind. ...
STAR TREK IV: THE VOYAGE HOME.
(Aka, "the one with the whales.")
There are people who really like THUNDERBALL, too, although, personally, it's not my favorite Bond movie . . . .
See, I never got the appeal of that movie. It didn't even really feel like a Star Trek movie to me. It's kind of light-hearted fluff, which is not what I look for in a Star Trek film.