I'm not necessarily asking for the scariest one you've played but for your personal favorite/best, based on whatever criteria you choose. Games that are more horror-lite/spooky still count as well, so feel free to consider and include those.

With regards to your pick: what made it so good? In what ways did its use of horror add to your experience?

Given that a lot of horror relies on surprise, subverting expectations, or the unknown, please give spoiler warnings if you plan to discuss important aspects/plot points that might ruin the game for others.

What horror or dark-themed games would you recommend, and why? No spoilers please.

Steam: https://store.steampowered.com/sale/halloween2018/

GOG: https://www.gog.com/games?page=1&sort=popularity&tab=on_sale

Humble store: https://www.humblebundle.com/store/promo/halloween-sale/