What is a good, story-driven, open-world, RPG style game similar to games like The Witcher 3 or Skyrim?

Might & Magic VI: The Mandate of Heaven. A bit older than both games but it's aged very nicely and is still tons of fun to play.

Zelda
For open world, Breath of the wild is great
for story driven, try skyward sword

overall, I d choose BOTW because the story and openworld factors are both excellent

Fallout is great RPG that i play a lot. Although the theme is very different it has a lot in common with Skyrim. I also recommend Destiny or waiting for a new god of war....both arent exactly RPGs like fallout and Skyrim, but they have a lot of roaming and quests.

only know of one that i currently am playing and that is horizon zero dawn for the PS4. great storyline so far, pretty lengthy game if you actually do everything even still it is lengthy because you do need to do side quests and what not for skill points. it's open world but the world isn't too huge. the only downside to this game imo is the fact that there isn't much of a customization when it comes to weapons you only are given 1 spear which you can't upgrade really you can do 1 quest that gives it more damage and there are only 4 different types of bows i believe. with 3-4 different variations all of which are basically like an upgrade to the last one and are all used in the game at once to combo skills to kill the robot dinosaurs. they have slots to upgrade them which you can swap out and enhance the damage and same with the armor.

really reminds me of witcher 3 though the enemies are not easy to kill even if your firing weapons that do a lot of damage to that specific dinosaur it still takes a few shots just to kill them with you constantly dodging attacks or stealthing around for kills or whatever you have to do to kill them and they do hurt.

World if warcraft