This is probably the most underrated Star Trek movie. The general rule about Star Trek movies is that you should avoid every other movie. With the first one being pretty bad, and the second being excellent, the pattern would dictate that this one is going to be pretty crappy. And it is that stigma that this movie has to overcome.
Christopher Llyod as a fierce Klingon is a questionable choice. Having Doc Brown as a bushy-eyebrowed, ribbed-foreheaded Klingon who is a physical match for anyone is iffy. To then make him a homicidal maniac who kills his own crew when they upset him is to venture into the unbelievable.
This whole thing was directed by Leonard Nimoy, and it demonstrates that talented actors, who may be talented directors, should probably not try to direct a movie they are in. This will become even more clear as we see the rest of the Star Trek cannon, and the actors start taking turns directing to varying degrees of success. Leonard spends most of the film behind the camera, at least. As a result, he could spend more time directing and less time looking at himself in the lens.
Saavik, who we've come to know and tolerate as played by the young Kirstie Alley, is now played by a young Robin Curtis. I don't know why we don't see Kirstie in this film, and I don't remember seeing Robin in any other role since then. It's not like Walter Koenig has had a massive number of films or appearances since the Star Trek franchise, but I'm not sure he really needed much more, did he?
The basic idea for this is that the Genesis planet, which was created when Khan set off the Genesis Device in the Mutara Nebula, also managed to regenerate Spock's corpse. The idea is that the main players will get Spock's body and take it (along with McCoy, who holds his spirit) to Vulcan for them to put Spock back in his body.
The storyline feels like a kind of stopgap for getting the character back for the rest of the movies. The massive ship Enterprise, which has a crew of over 400 people, is easily stolen by a crew of 5 and the pursuit craft (run by a more massive crew who are all aboard) is stumped by the removal of a handful of parts by a guy who doesn't actually know its systems.
Nevertheless, the storyline is kept moving pretty well, aside from some of the Pan Farr nonsense on the planet surface, and the heroes somehow manage to beat the bad guys by outsmarting them again. Cheap tricks is how Kirk has managed to stay alive this long, and he uses more with some added luck to keep his streak alive.
The storyline is a bit sketchy, but tolerable
The acting is good, for the most part
The dialogue is good
Directing was not great
Special effects were more of a mixed bag than in the other movies
2.75/5