[without spoilers] I just finished my first playthrough and was quite surprised to the attention to detail to all the secondhand story telling and the mystery of it all. Excellent general ambience and attention to detail!
[minor spoilers] I'm currently on another run trying to see how my actions impact the events in the story, and noticed quite a profound feeling as I'm physically writing things down trying to truly solve this mystery, and doing all the same theory crafting that people did with fnaf all those memories ago. It's so nice to feel that again.
As for the creature and the scares, the window dragging sound ended up being more of an annoyance than anything, after I figured out it wasn't of any real threat, and the creature in the box (which I presume is the bad ending?) wasn't really an impactful scare, as all the suspense kind of built up for a half baked reveal. I will update the things I might've not understood on my first playthrough as I continue to solve this mystery