Fail-safe is a very short SF adventure, containing one big puzzle, some less than stellar (but by no means bad) implementation, and a very brief story. That may not sound like much, and it isn't much. But what makes the piece is how it experiments with the relation between the player and the narrator.
This is impossible to discuss without spoilers, so I suggest you play it before reading on.
(Spoiler - click to show)Fail-safe has an unreliable narrator. Not just that, it has a narrator that actively tries to trick the player (or rather, the narratee) into forming a wrong idea about the world. If she does form the wrong idea, the narratee will take an action that will be great for the narrator but disastrous for herself. The puzzle consists in the player (a) finding out that the narrator is lying; and (b) responding with an appropriate double bluff. Great stuff that I would like to see explored further in a more substantial game.