Without spoiling the experience it has quickly become one of my favourite games of all time. You play as Stanely, an office worker that has spent his working life pushing buttons, then one day the code he has to input stops. Stanely finds himself alone in the building and must find out where everyone has gone, and thus his adventure starts. The whole game is voiced over by a narrator, every object you interact with and every turn you take is commented upon with a Monty Python esque quality. The game never seems to end, with hundreds of variations on the way Stanely's adventure plays out. For example you can close the door to your own office at the very start and that's it, the narrator comments that Stanley waited there until he dies and the game restarts, that was just one of Stanley's stories. The game constantly breaks the forth wall with the narrator talking directly to the player and questioning their motives, eventually question the very nature of gameplay and even more philosophical matters.
I certainly recommend it, even if you just download the demo from Steam, in fact the developers have made the demo a completely different experience so you don't spoil the full game. The developers also released a video, based on a letter they received from a player, who was criticising the game. The player clearly doesn't understand what Galactic Cafe were trying to do with the game, but the video really showcases the sense of humour that the Dev's have, and which is prevalent in the game.