I once played a video game in which the only meaningful user interaction was making a choice between two options about halfway through the story. (The "non-meaningful" interaction was clicking to advance the cut scenes and conversations.) I think that was pushing the boundaries of "game".
Since someone mentioned Cow Clicker below, I have to also throw Progress Wars into the conversation. Also created as a satire, and rather amusing to play a few levels (despite being intentionally non-fun).