Five Nights at Freddy's. Amnesia. Slender. Outlast. Any/every horror game released in the last few years that has become The Thing™ to LP.
I probably wouldn't even like FNAF or Slender. But I had so much trouble getting through Amnesia and Outlast after, unfortunately, stumbling upon their crazy LP-based fanbases.
Though Amnesia was already ruined for me after witnessing several Penumbra vs. Amnesia wars. Guys. Guys they were made by the same people. stop it.
Another fanbase would be the Resident Evil fanbase. They haven't ruined the series for me, but they did ruin the Resident Evil community for me to the point where I can't take almost every one of them serious. Always arguing over what is the scariest RE game, what is RE and what isn't, what makes RE scary, going philosophical about RE, complaining about getting exactly what they want, complaining how the series is dead because Resident Evil 4 "ruined everything"
^ This, for both Resident Evil and Bioshock.
They both suffer from the same crap that divides the fanbase: Which titles are or aren't a RE/Bio game, which title "broke" the entire series for them, which titles are or aren't scary, etc.
Didn't ruin the series for me, ofc. But it did make me take way too long to get around to playing Bioshock 2, which is a shame.
Case in point: Twitch Plays Pokemon Red had like 100,000 followers, which dropped to maybe around several thousand in the playthroughs of the more recent games.
What does that have to do with anything. Just because they
started in Gen 1 and then people got bored of the idea so their followers dwindled? That doesn't automatically imply that most of the followers only liked first gen.
It's not like they stopped watching a competent LPer with interesting/funny commentary play through the games - they stopped watching a gimmick that gets old after awhile. Even with a competent LPer, Pokemon games are hard to watch. Anything turn-based is pretty boring to watch, and much better suited for a screenshot LP than a video LP.