On the face of it, Doki Doki Literature Club looks like every other Japanese visual novel/dating simulator that have recently been flooding the Steam market. The tags of "Psychological Horror" looks like people are just trolling, but the game's description does have a content warning: "This game is not suitable for children or those who are easily disturbed." which is also displayed when launching the game.
You are a guy that has joined a book club purely to keep your female friend happy. There's three other girls there which seem to be fighting for your attention. They all seem to have their quirks and insecurities, but your character is sympathetic. It takes a few hours for things to begin to take a turn, then it escalates from there.
It's hard to describe the game's content without spoilers, but lets just say the story is intriguing and it has some moments like Eternal Darkness where it breaks the fourth wall and messes with you.