Trying to think of Trek episodes I really enjoyed and that are generally considered to be "good"
Balance of Terror
Best of Both Worlds
The Visitor
Darmok
I wonder how they would fit in this argument....
These are all character stories, or the character stories justify their existence. BoBW may have started with the big idea to have a huge Borg cliffhanger, but once the story process began, it was written from a perspective motivated by character.
Balance of Terror: A character drama about how war destroys people and sabotages relationships. Kirk and the Romulan commander would have been friends without war, Styles might not have harbored his bigotry, and Angela Martine and Robert Tomlinson would have survived and had the hope of a happy marriage. We learn a lot about all these characters, and how they react to things.
Best of Both Worlds: A story about Riker's ambivalence about taking on a captaincy of his own. He gets pushed further to think about it than ever before, first by Shelby's transfer, then by Picard's assimilation.
The Visitor: By far the most character-driven of all of these, it uses a science fiction premise to delve deeply into the relationship between Jake and Ben. Not only is this episode important as a stand-alone, it underscores how unready Jake is for Ben to leave, and how much he has to grow up by the time Ben finally does leave.
Darmok: Similar to Balance of Terror, it's a character drama that's almost the flipside of Balance of Terror's tragedy. Here, Picard and Dathon actually get to bond as the friends Kirk and the Romulan commander wanted to be.
Just for fun, some of the other universally-acclaimed stories certainly fit as well:
City on the Edge of Forever: We learn what line Kirk is willing to cross in the tension between love and duty. We even get to know Keeler quite well.
Amok Time: It's not just about Spock's arranged marriage, but about Kirk's utter devotion to him. The beautiful line "Isn't that worth a career?" speaks volumes.
The Trouble with Tribbles: Largely a farce, we still see Kirk's frustration and handling of bureaucracy, but everyone gets great moments.
Duet: How much can Kira forgive?
Far Beyond the Stars: An episode about Sisko further coping with his increasing visions as Emissary, as well as the important themes on representation.
Year of Hell: A tragedy about Annorax.
Cogenitor: Character, character, character.
Similitude: Character, character, character.
The Forge trilogy: Archer's journey toward understanding Vulcan, Soval's journey toward understanding humans. T'Pol's closure on her relationship with her mother.