It doesn't classify itself into horror, or sci-fi genre in the way of most current shows or movies. This series isn't about jump scare or shock value. It's not paranormal activity in how you would think of how a supernatural horror story would happen. It's a haunted series of current events and flashbacks that explain itself as it progresses rather than being a complete narrative. For several episodes I didn't understand the present events that related to flashbacks. Watching most of this series I was watching with a mindset of waiting for a cliche moment. (I.e something predicable like a jumpscare 3 seconds after a quiet moment.) I was impressed by the ability to abstain from predictability and shock value, and have it tell a story and paint a picture. Through 8 episodes I never realized all the hidden ghosts in the background of scense that are sometimes very noticeable. The reason I didn't notice them is because of excellent visual direction and distraction. Your attention is so focused on what's happening in each scene that you miss everything else in the scene.
By far my favorite Netflix original horror/supernatural anything. Movie or series