If there really was a Penumbra craze I wish I was there, unless you meant Amnesia. Amnesia was quite a craze when it came out and it got PewDiePie to where he is, in fact a lot of Youtubers started out with this game. I was kinda hoping SOMA would be more like Amnesia and create a new craze but it isn't as scary.
OT: FNAF is still very popular fodder to stream or make videos for, but the game can only stay fresh for so long. Its only natural that the craze is slowing down, by the time the DLC releases I'd expect another small craze.
I do think that Scott should be giving more time between their releases and just try to innovate more with his new games.
Doesn't really matter if it's the same, he pushed out a few games in a short time because he had to make profit while the hype lasted. During a hype it doesn't really what a certain franchise releases, as long as people can talk about something new it's good enough.
You can compare it to Dark Souls, if Twitch hadn't been around for Dark Souls 1 you can rest assured that Dark Souls 2 wouldn't have been released for another 3+ years at the very least. The difference ofcourse is that Dark Souls ish games bring something to the table even if it is just amazing scenery compared to FNAF.
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Amnesia wasn't actually that Scary, it was immersive though. The last really scary game I played was Outlast...
Playing Soma atm, liking the start but I'll admit the monster chase element isn't as strong as in Amnesia 1 (Amnesia 2 was terrible as a horror game, great as a story game)
It happens to most of those types of games really, and especially with something like Five Nights where there isn't a ton of depth or engaging replayability. Look how huge Rocket League was and it's really fallen off quickly. It's #43 on Twitch right now behind games like Sonic Heroes, Pokemon Ruby, and Toilet Tycoon (no joke). And Rocket League is a bigger budget than Five Nights game, with mp, and far more replayability. And it was given away in PS Plus.
It would be pretty easy to come up with a long list of Indie Steam games that were quite popular for a short time and have fallen off.