As with any classification, the reality is often putting things on a sliding scale, and one product can have game modes or chapters that belong to wildly different categories. It's also possible for players to completely ignore the structure, step outside the path we laid out, and even make up their own goals. For example, some players in GTA 5 may completely ignore the tight sequence of story missions concerning the main characters, and instead explore the world, set records in longest car jumps, and try to attract as much police attention as possible and get away with it.
Settling for a particular style of game structure within any part of your game is an important part of the design process. You need to consider:
