I just watched the first episode of Netflix's Dahmer, and it's terrifyingly scary.

First of all, because it's a true story, the sense of realism and immersion is overwhelmingly stronger than any ghost or monster, and the actors' performances are incredible.
It doesn't rely on explicit depictions, but rather crushes you with sound and atmosphere; the sound design, in particular, is disturbingly well-crafted.
The visuals are expressed so grittily that you can almost smell the stench through the screen.
It perfectly captures that beast-like feeling of a psychopath who is impossible to reason with.