the story: Klingon civil war breaks out thanks in no small part to Romulan instigation, leading Worf to make a difficult decision.
similar to: "Way of the Warrior" (Deep Space Nine), "The Expanse" (Enterprise)
my thoughts: In many ways, "Redemption" is far more important to Next Generation's legacy than "The Best of Both Worlds." Where the latter is plenty iconic, "Redemption" defined in large part the show's legacy, which can be felt in each subsequent Star Trek series and in television generally. It's the point where serialized storytelling became more important than serialization, not because of soap opera qualities or some general goal, but because the mythology of a concept became the most important aspect of the storytelling.
I'm incredibly tempted to write a whole article on the predecessors and successors to "Redemption," from Next Generation itself, from other series, other movies. It's a legacy that quickly eclipses "Best of Both Worlds." It's really that important.
For starters, it introduces the Duras Sisters, Lursa and B'Etor, who end up impacting the franchise in ways the far more limited and utilitarian Duras himself ever could. They appear throughout the remainder of the series, in Deep Space Nine, and join Khan and the Borg as familiar figures to appear in the movies when they meet their demise in Generations, always scheming but in increasingly unpredictable ways. In a lot of ways, they're the true legacy of Harry Mudd, and they're a lot harder to forget.
If you start only from "Sins of the Father" and "Reunion," in which Worf enters the Klingon fray more directly than at any other point in his life, "Redemption" expands those developments and builds on them. In Star Trek lore, Klingons have opera. In the episodes themselves, this is the Klingon opera, a crescendo of all the best work the series had done to this point, and in a lot of ways, the rest of it was kind of a letdown, never really trying something this ambitious again (there's the realm of Deep Space Nine).
This is the meat and potatoes of the franchise mandate, coming to terms with an alien culture, in ways the original series and Spock could only play at, even in the movies. Worf's conflicts are indeed epic. Although he does return to Starfleet, the fact that he leaves at the end of this episode and season is completely unprecedented, and prove the depth of his character and the series around him.
This is a culmination, besides, of the rich character work that was the season at the peak of its creativity, and it successfully and artfully weaves high drama around a main character and significant guest stars around him, something that had heretofore eluded both the season and series so far, so often with one or the other dominating, but never both at the same time.
And the story only gets better...
criteria analysis: franchise - series - character - essential (all criteria met)
Robert O'Reilly (Gowron)
Tony Todd (Kurn)
Barbara March (Lursa)
Gwynyth Walsh (B'Etor)
Whoopi Goldberg (Guinan)
Denise Crosby (Sela)