The Stanley Parable is an experimental narrative-driven first person game. It is an exploration of choice, freedom, storytelling and reality, all examined through the lens of what it means to play a video game. You will make a choice that does not matter You will follow a story that has no end You will play a game you cannot win ...it's actually best if you don't know anything about it before you play it :D
By far the single best mod I have ever played. It's like Portal, but even more story intensive. It basically changed my life.