IncGamers - Open-World Evolution Column.
Now, though, most open-world games do have a linear order. If I say open-world, it probably conjures images of Grand Theft Auto, Just Cause, Saints Row, Prototype, Infamous, and so on and so forth, which are linear games that give you a huge “hub” with plenty of side missions and hidden bonuses to occupy your time. The illusion, usually, is that you're in a living, breathing world that you can impact in a variety of different ways at any given time, even if your ultimate goal is to progress through the entirely linear set of missions that make up the core gameplay.