The Stanley Parable begins with an in-engine cut scene set of a man in a dingy office. A narrator explains that this is Stanley, who loves his job, even though as described it sounds quite tedious. But, we are told, one day the orders he receives on a screen stop coming, and he realizes that no coworkers have stopped by all day. So he decided to go to the staff lounge.
At this point, we are handed the controls. The office opens onto a corridor. The narration continues when we hit certain points along the corridor; and eventually, we reach a branch, and are told that "Stanley turned left."
Following the narrator's instructions eventually leads to a story in which, supposedly, Stanley liberates himself from a control device that kept him happy despite the tedium of his work; and, in a final narration, are told that "Stanley would never follow orders again." Which is amusingly disconcerting because, of course, to reach this ending, we did nothing but follow orders.
Naturally, if you restart, and diverge from the path, the story changes -- quite often, the narrator becomes prickly and upset with you, because you're not doing what your told. There are, of course, multiple different endings depending on what path you take -- some rather humorous.
What's interesting here is that there is a narrative experience, even though the environment is quite sparse and there are no characters, other than "Stanley" -- carried, basically, entirely through narration. It is, in essence, a hypertext story, a branching narrative in which branch choice is made by navigating in 3D space (The Stanley Parable is a Half Life mod). And a pretty amusing one.
Only arguably a game, of course, but like many, I've gotten tired of the "game/not game" argument.
You need a Steam account to download; the readme file provides instructions for how to install and play.