[SPOILERS]The trump-card of The Search For Spock is how it's a direct sequel to the clearly-superior Wrath Of Khan. Therefore, taken as an extended denouement to its illustrious predecessor, it's essential and enjoyable viewing (if only to see the Genesis storyline conclude properly) and it works fine as a piece of entertaibment, despite its unshakeable stigma as one of the "odd-numbered Trek" misfires.
Leonard Nimoy -- who had only returned as Spock for Wrath Of Khan on the understanding his character would be killed -- clearly had second-thoughts after seeing the finished product (which included a get-out clause to make Spock's resurrection possible, fortunately.) Star Trek II was a huge success at the box-office and encouraged Paramount to push ahead with a third film, with Nimoy himself installed as director, working from a script by Khan storywriter Harve Bennett.
The Search For Spock finds the battle-scarred Enterprise limping home to space-dock after its nebula skirmish with Khan, only for Kirk (William Shatner) to discover his beloved ship is being decommissioned to make way for sleek prototype the USS Excelsior. Meanwhile, Kirk's son David (Merritt Butrick) and Saavik (Robin Curtis, replacing Kirstie Alley) return to the newborn "Genesis Planet", where they discover Spock's corpse has been resurrected into infant form as an unforeseen side-effect. Not only that, but Dr. McCoy (DeForest Kelly) has unwittingly become the receptacle for Spock's "katra" (soul), and begins exhibiting strange, Vulcan-like behaviour aroud the space-dock, necessitating his confinement to quarters.
Fortunately, Spock's saturnine father, Ambassador Sarek (Mark Lenard), arrives and explains McCoy's strange behaviour -- giving Kirk hope that his friend's body and soul can be united in a Vulcan ceremony. But, time is of the essence; so, with the help of his always loyal crew, Kirk smuggles "mad" McCoy out of Federation custody and steals the Enterprise to fulfill their mission. But, lurking in the depths of space as an added complication is Commander Kruge (Christopher Lloyd), a Klingon who's learned of the Federation's Genesis experiment and, in an unfortunate echo of Khan, aims to steal the technology and use it as a weapon.
Star Trek III doesn't deserve its poor reputation, really, although it's by-the-numbers moviemaking that doesn't hit too many highs. The main issue is that it's designed as a way to renege on Spock's death, thus giving audiences a sense of frustration that this isn't a brand new adventure. Certainly, beyond some fun moments with a "possessed" McCoy and the exciting capture of the Enterprise (including the comical sabotage of Excelsior), there's not much to grab audiences until the third Act, when events all come to a head on the disintegrating Genesis planet...
For all its first-half faults, Star Trek III actually contains two moments that rank a some of the finest in the canon, like: the emotional self-destruction of the Enterprise (you officially lose geek-cred if don't get a lump in your throat when Kirk watches his ship trailing comet-like across an alien sky), and the gut-wrenching moment when a Klingon savagely murders Kirk's only son with a knife to the back. Shatner himself claims his wounded reaction to David's death is his finest moment in Star Trek, and I can't really argue with him. It's also a moment that sparks Kirk's understandable hatred for Klingons; a trait the writers should probably have woven into his psyche years before, but is only utilized three movies later during Trek VI.
So, while by no means a great entry into the Trek pantheon, it's not as awful as you probably remember it being. This was actually the film where the crew started to feel a fun, likeable group (as Trek II was primarily focused on Kirk/Khan rivalry), and it successfully builds to a strong finish that helps dilute the plodding first half. Mind you, it's always confused me that Kirk essentially spends the whole film acting in defiance of Spock's mantra ("the needs of the many outweigh the needs of the one, or the few") by risking everyone's lives to get Spock back!
Paramount Pictures 105 minutes
Director: Leonard Nimoy Writer: Harve Bennett
Cast: William Shatner (Admiral James T. Kirk), Leonard Nimoy (Spock), DeForest Kelly (Dr. Leonard "Bones" McCoy), George Takei (Hikaru Sulu), Walter Koenig (Pavel Chekov), Nichelle Nichols (Uhura), James Doohan (Montgomery "Scotty" Scott), Bibi Besch (Carol Marcus), Merritt Butrick (David Marcus), Mark Lenard (Ambassador Spock), Judith Anderson (High Priestess T'Lar), Robin Curtis (Lt. Saavik), Christopher Lloyd (Commander Kruge), Robert Hooks (Fleet Admiral Morrow), James Sikking (Capt. Styles) & John Larroquette (Maltz)