Where it should have been on the list: #38, so a tolerable middle-of-the-road episode that sometimes approaches "good."
In case you forgot: The Power Trio is tasked with negotiating an agreement with the aggressive, semi-barbarian residents of Capella IV over topaline. Unfortunately, the Klingons have gotten there first, poisoning the well and sending the Enterprise on a wild goose chase. The leader, Akaar, is sympathetic to the Federation but gets assassinated, leaving the Power Trio and Akaar's pregnant widow Eleen in a precarious spot. All four escape, McCoy delivers Eleen's baby, and the Enterprise returns just in time to help oust the Klingon scout and install Eleen (and baby Leonard James Akaar) as the new leader.
Clearly some thought went into creating the Capellans and their culture, more than in some other aliens of the week. I can appreciate that, even if their costume design is pretty silly. I also like that Eleen ends up in charge of the Capellans, though whether this will set a better precedent for Capellan women or whether it will just be an anomaly in their history is hard to tell. Overall, the story doesn't lack for action or intrigue: there isn't anything in the way of filler here (except maybe shots back on the Enterprise during its wild goose chase).
There's just a bunch of random little things keeping this episode from being better. The costume design is just so silly in this one. Everyone looks like Muppets! It kind of detracts from the seriousness of the story. Then there's the final confrontation; with people forfeiting their lives in exchange for others and crazy distractions and so on, it's a bit garbled, even in the re-watching. You also have to wonder if the Prime Directive applies here, since Kirk is totally cool with people waving their phasers about in front of a more or less primitive culture. And even though it's "culturally acceptable," it still feels damn weird to see Bones slap a woman.
Some trivia: this is the first appearance of McCoy's "Dammit Jim, I'm a doctor, not a ____" catchphrase.