I don't think open world is really a genre. It's a game design element that can apply across genres. So, for instance, you can have a highly linear RPG (FFX), or an open-world RPG (Oblivion). Or, to take mc's example, you can have a more linear Tony Hawk game or an open-world one. But if you just say that a game is open-world, it doesn't tell anything about the gameplay, which is what genres do.
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You put your RESOLVE HAT back on, which conveniently is the same hat as your NORMAL HAT.
{Drakeryn}