Not a failure and not mediocre; here's why
The Search for Spock is a great Star Trek picture embellished by the welcome return of Trek’s quirky brand of humor after two serious movies. The story expertly meshes comedic touches with dead-serious tragedy. It’s also enjoyable and compelling to witness Kirk & crew in the wry and unexpected role of Starfleet rebels, risking everything to honor their fallen comrade. Another highlight is the return of the Klingons as major villains, with upgraded make-up no less.
The only problem with this pic is revealed in the title — there’s no Spock. At least not until the very end; but the film does a fabulous job of instilling a sense of the Vulcan’s lingering presence throughout.
At the same time, this proves that Star Trek is greater than any one character: Just as Spock’s absence in this film doesn’t prevent it from being great, so Kirk’s absence from the main storyline in the 1st Season's “The Galileo Seven” doesn’t keep that episode from greatness.
The Search for Spock climaxes with the powerful image of Spock’s mates gathered around the freshly-resurrected Vulcan. This scene is well worth the wait; all Spock has to do is raise an eyebrow to fill the viewer with warmth and joy (and maybe a few tears as well).
Lastly, I gotta hand it to the creators for coming up with an inspired and (seemingly) credible way to resurrect Spock; the Genesis device was, by happenstance, the perfect catalyst.
Sadly, Star Trek III is inexplicably condemned by fundamentalist Trekkers as a failure or, at best, mediocre.
They’re wrong.