Star Trek: Enterprise
A dude becomes pregnant. Honestly, I think doing an episode like this so early in the series made it hard for some people to like Enterprise above and beyond any other reason you may have heard or had.
But the thing is, it's not just some random dude, it's "Trip" Tucker, and it's exactly this kind of experience that helped define him, ultimately, as one of the best characters in the whole Star Trek franchise. Because of his accent, Trip was sometimes pegged as the McCoy stand-in, a country outsider looking in as the wonders of the universe came pouring in. And yet, Trip was always more of a Kirk. With a crucial difference. Whereas Kirk routinely let experiences roll off his back (with a few exceptions, and probably an era that ended with Spock's death) and led the way with a smirk, Trip tended to stumble his way forward, undaunted but routinely inconvenienced. He couldn't help but let things get to him.
The biggest impact on his life was when Trip's sister died at the start of the Xindi arc. It ended up defining him for at least a season, trying to get over it. Remember in Star Trek VI: The Undiscovered Country when Kirk admits that Klingons weren't just his enemy by default anymore, but personally so after the murder of his son David? Trip existed in this mode from the start. He was Enterprise's emotional anchor.
So yeah, when the final episode ("These Are the Voyages...") comes around and spends most of its time exploring his impact, I tend to overlook things like how much time Riker and Troi got, because it's not a Riker and Troi episode, it's a Trip episode. The final episode of the series, dedicated to Trip, not Captain Archer. I think that says something right there.