Star Trek: Voyager
Hey, you remember Battlestar Galactica, right? Not the original version, which was more or less a blatant knockoff of Star Wars (this time with more Lorne Greene!), but the reboot, which was more or less a blatant knockoff of..."Year of Hell" (this time with more Edward James Olmos!).
Ha! Just kidding. But seriously, the early episodes of Battlestar Galactica (as opposed to the later episodes, which were much more about revealing secret Cylons [no one suspects the Cylon invasion!]) were all about humanity's desperate bid to survive against incredible odds, real grim and gritty presented with grim and grit (and sexy, sexy Cylons). And genre fans loved it. Battlestar Galactica was, in short, the latest in a long series of genre programming that was, basically, Not Star Trek.
By 1994, just when everyone thought Star Trek was going to finally become cool, Star Trek's own fans began turning on it. In effect, Star Trek, which was already massively uncool to the general population, became uncool to its own fans. These deserters started seeing how genre programming was being done by other people, and began to consider Star Trek outdated. Does it matter that after Next Generation left the air, this left Deep Space Nine, which did make a conscious effort to switch things up? Not at all, silly person asking questions to someone typing without the ability to hear you and thus must conjure your existence into being! You see, Deep Space Nine was seen as a ripoff of Babylon 5. Mostly because, y'know...they both...had...space stations. And stuff.
Emphasis on "and stuff."
So when Voyager rolled around and pretended to change things up even further but really rebooted back to what Next Generation and the original series had been doing all along, the fans rolled their eyes further into their head, causing a massive migraine that did not dissipate until Star Trek Into Darkness.
Basically, Voyager pulled an evil trick. It pretended it was going to be all grim and gritty, but then, quite evilly, made Captain Janeway able to make peace with a bunch of Federation dissenters and make one big happy crew...stranded decades from home, a lifetime away at first estimate. What to do, what to do???
"Year of Hell" was the two-part episode that had a look at what it would have been like for a true worst-case scenario to occur (unlike the episode "Worst Case Scenario," which merely had a look at what would have happened if those pesky Federation dissenters, the Maquis, had decided they hated Janeway's hairdo as much as everyone else). Gradually, everything went wrong. The ship fell to pieces. The crew splintered. Janeway ran out of coffee. Tuvok went blind and thus could no longer...(never mind about that!).
Basically, substituting Seven for Number Six (imagine that!), "Year of Hell" is exactly what Battlestar Galactica would be (for a handful of episodes, as well as the perpetual grumpiness of Adama) years later.
We're right back at the start! Yay!