Gamasutra: The History and Theory of Sandbox Gameplay

So I learned that “sandbox” is the name for what I’m thinking about. And I’m not the first to think about it. Surprise, surprise.

The main reason that this trend towards believable characters is compelling for sandbox play is that the characters are, at bottom, more dynamic and interactable. They help “sell” the game world because they seem more realistic. Not “realistic” in the sense that they can ever hope to pass the Turing test, but realistic enough that they’ll lull you into forgetting about their artificiality. The more intelligently the NPCs respond, the more the game feels like a free and open world.

Full article