Open world isn't a genre. Just about any genre can have open world or linear games, or things in between.
Open world is like 2D vs 3D. Though in the case of open world it doesn't really open up a new vista of gameplay styles as it is merely a setting rather than a perspective.
The funny thing about open world is that most people really don't want truly open world. What they want is freedom of movement. You wouldn't call resident Evil Open world, but what it allows you to do is go back and forth from area to area whenever and however you chose, i.e. back tracking and side tracking. Linearity does not allow much back tracking, and allows almost no side tracking. A truly open world is normally a pain in the arse because you spend so much time travelling form point A to point B with nothing particularly interesting happening in between. And that is why pretty much every open world game, and lots of semi-open world games, have fast travel, so you can avoid the boring bits, which basically turns the open world into a series of smaller open areas with the illusion of long distance travel.
I'm sure this generation will have its bandwagon, and it does seem open world, or non-linearity might be it. Though if a game like The Order can sell well enough to earn itself a sequel, and if Uncharted 4 is only slightly less linear than the PS3 outings perhaps open world / non-linearity might not become the new meta and it will sit comfortably among all the other perfectly legitimate approaches to game design. All choices are good, so long as there is variety in the game library, and the quality and quantity provides most buyers with an experience they regard as value for money.
If open world becomes the new thing, at least that's a format I can enjoy. I hated the FPS heaviness of last gen, though there were still plenty of non-FPS games to be enjoyed.
“The fundamental cause of the trouble is that in the modern world the stupid are cocksure while the intelligent are full of doubt.” - Bertrand Russell
"When the power of love overcomes the love of power, the world will know peace."
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