This highlights how people mean different things by open world. Windwaker HD and Deus Ex are my favourite open world games.
What most people seem to talk about when referring to open world are the elder scroll esk games. Large world where you can head almost anywhere early on and complete many countless sub-quests. Not may favourite types of game typically. I enjoyed fallout 3 but I don't get the scale of the hype for fallout 4.
I thought Xenoblade Chronicles was an interesting take on open world as in many ways it was a very linear path following the main story but you could stop in any of the vast areas on the way, should you choose, and optionally explore the many subquests. Which I chose to largely ignore. I thought of Deus Ex in a similar way. Many small openworld sandbox areas tied together with a largely linear (With a few minor branching variations) central plot.