Personally, I find the lore very interesting. It's a dark story for a game like this, but there's so much to it, ya know? You wanna keep learning more and more about what happened and piece all the clues together.
Also, even though jumpscares might be "cheap" scares, I really felt like the 1st game was a unique take on horror games. Sitting and waiting for something to get you, rather than going out and finding it. And I like the animatronics (even though they're trying to kill you). Foxy is my fav.
For something so simple, I felt it did a great job in creating suspense and basically keeping you on edge. Of course after a while, you'll get used to it and not really worry too much about most of them. For me though, I still chicken out on night 4 because of Freddy. I never got passed night 2 on the 2nd game cuz Foxy kept killing me. ;_;
But yeah, the lore is the main draw for me. I love games that make you think. And by that I mean, it provides clues and hints and such about the story, but doesn't outright explain. Thus many theories come out of it and it's fun to talk about. =)
Although...the downside for me is the fanbase and how Scott released them so close together. I mean FNAF's 3 came out only a few days ago and there's YTers that hurried up and beat it IMMEDIATELY. Not enjoying the experience at all. This series just gets milked like crazy and it's just a game to say to played, rather than have fun. Least that's how it feels. And now that there's tons of clones, I've honestly gotten really annoyed by it and didn't get too excited that a 3rd game was getting made. How much more could Scott do? He just kept the same formula over and over and it got stale.
Sorry for the long post, but all in all, I do really enjoy this series. I just think it coulda been handled better and given more time to improve upon what made it popular in the 1st place.