I have real love for TNG S1E16, "Too Short a Season."

The Enterprise is dealing with a hostage crisis on a planet where the local government wants this old admiral who had negotiated a truce there decades before to come back. He shows up and it turns out he's taking experimental de-aging drugs to grow younger. It turns out that when he had negotiated the original truce before, he had violated the prime directive and given weapons to some rebels, but he told himself that he made it even by giving the same weapons to the other side, which led to decades of bloodshed.

The writing is just okay, and the old guy / young guy makeup is pretty bad, but the scene where the admiral dies while looking into his wife's eyes gets me. I also like to imagine that the ep might have originally been written with Kirk in mind as the old guy, because the whole "Well I made it fair by giving weapons to both sides" seems like the kind of cowboy insane shit that Kirk would pull and then never consider the consequences. The episode feels a little bit like it's revisiting some of the times when Kirk would do his thing and then warp off into the sunset while definitely leaving some loose threads behind.