[Slightly Spoilerish] Without even having seen David Robert Mitchell previous movie "The Myth of the American Sleepover" I'm quite certain that both movies have some similarities despite the first one not being a horror movie at all. I also think that is one of the main factors when it comes to this film, it doesn't feel like your typical horror movie while still showing off it's influences.
The big bad here is just "It" - a being taking the form of someone known to the victim who is slowly but steadily walking toward it's target. The only way to get rid of it is to have sex with someone else but if whoever is on top of it's list dies it falls back in the chain. Simply put: If you can't deal with it, fuck someone else and better look for someone who can either handle it or has a high chance of passing it on too.
Unlike many teen horror movies the girl who "gets" it and her group of friends are written more realistically and go about it reasonably. Unfortunately it seems that no one in the curse chain was creative enough then despite it being not completely dumb there seem to exist more than enough methods to keep "It" in check.
Nonetheless, it's a solid movie relying more on atmosphere than a body count or jump scares.