Defcon: Everybody Dies has one of the best ambient atmospheres for a game.

You must listen to the soundtrack. It is a background of recycled air, radio chatter, static, and a soprano singing... perhaps of your loneliness. You can't help but feel like you are in a remote bunker pushing the button to end millions of lives. Then suddenly, you hear the faith sounds of a women crying... is she crying about someone who just died?

Disturbing.