The game seperates itself from Ubisoft Open Worlds, why do people keep saying this? You are making incorrect assumptions, but whatever. See the quote from the review below:
http://gameaxis.com/reviews/horizon-zero-dawn-playstation-4-masterpiece/
Unlike many open world games, Horizon: Zero Dawn doesnt bog you down with repetitive and mostly unnecessary side quests that risk overwhelming players heres looking at you Assassins Creed and Far Cry.
Not to mention it's an RPG, with Lore, Dialog, and unique combat against a unique enemy. Seems you made your mind before.