Know any "Can't tell you anything about it, but you NEED to play it!" games?

We all know movies and games that we just can't describe to people without spoiling something.

The first rule about that game is: you do not talk about that game.
   -Albert Einstein, 1492

In terms of movies, I can think of Memento, The Man From Earth and Fight Club.
In terms of games, I'd venture to say The Stanley Parable and The Witness.
I would tell you all about them, but I really wouldn't. For your own sake.

Are there any games that I NEED to play, but that you can't tell me anything about?