I don't often have patience for the "slow burn" horror movies, but that's because so many entries into that little sub-genre of horror don't actually have the goods to back up their approach, and often seem to do it simply because their budget ran out or they needed a way to pad out the minutes.
Pyewacket is successful in its attempt to build suspense and tension though, and the cast, script, and direction are good enough to hold your attention until the end despite the fact that very little is actually directly shown in terms of the evil presence at work here.
It's not going to blow your mind, but it's a solid, relatively well-crafted story with a memorable ending.
P.S. Don't listen to that ridiculous 1/10 kid's review that claims you need to be "a professor" to understand this one. This is absolutely not one of those movies with some complex meta plot that you need to rewatch to be able to catch everything. It's 100% straightforward and literally explains right to the viewers' faces what is happening. You shouldn't have any trouble whatsoever understanding this movie unless you ride the short bus.