The Five Nights at Freddy's series is, for some reason, a huge hit at my kids' school. They talk about the game, they get excited about each new version and they love watching people play the game on YouTube. These are kids barely on the edge of being teenagers, by the way.
The above episode of PBS Game/Show goes into great detail about what the game does well and why it's so easy and enjoyable to both play and watch, but it's the generation gap aspect of the game's popularity is interesting to me.
It's the perfect storm of anecdotal evidence about how children play games. They love their mobile devices, and they think consuming the act of someone else playing via YouTube is a great way to interact with their favorite games.
If you haven't played any of the series, give it a shot. They're not bad, although most of the enjoyment other people find is a bit lost on me personally. If nothing else, you may learn a bit about what those kids are into these days.