I think 'open-ended' would be selling it short. A Halo 'combat arena' is open-ended. The Sims is absolutely an open-world game. The simulated (game-)world is o

I think 'open-ended' would be selling it short. A Halo 'combat arena' is open-ended. The Sims is absolutely an open-world game. The simulated (game-)world is open to the player -- they are free to interact with it as much or as little as they like, in a manner of their choosing. Importantly, the simulation will proceed (in meaningful ways) with or without action by the player.