Ah, this game scared me so much that it made me poop my pants. Anyway, let's talk about what made this game terrifying. For me, the terrifying part is the behavior of the animatronic mascots.
It's terrifying at first, but after several days of playing it, you get desensitized to the environment. It doesn't help that you know when you're going to get a screamer--it's a scripted action.
its a very fun game and to me i suggest looking up some of the lore on this game after beating it. There are tons of theories and some awesome easily missed hidden stuff on this game, i suggest going to Mrcreepypastas channel and watching his stuff on it, either that or game theories five nights at freddys video. as far as gameplay itself, its very simple but enjoyable. no real replay value though, however it still creeps me out somewhat. the five nights at freddys 2 is worth playing as well