As someone who has played every single Dark Souls game, I'm aware of the fact that Dark Souls allows exploration. Point is that allowing for exploration does not simply make a game open world. You can, for example, explore the world in Ocarina of Time to your hearts' content, but very few people, if any, consider it an open world game.

What separates an open world game from a game that simply allows exploration is how interconnected the world is. For example, let's take Dark Souls 2 and Just Cause 3. Choose any area in the game in Dark Souls 2, and the number of methods to get there outside of warping will be limited. Let's use No Man's Wharf from DS2 as an example, although this can really apply to just about anything. If you want to get to No Man's Wharf, you have to pass through either the elevator from Heide's Tower of Flame, or ride the boat in from the Lost Bastille. That's it. Those are the only two entrance points. It's a sectioned off area, and there is no other way to get in outside. Just about every area in the Dark Souls series fits inside these guidelines; a very limited number of entrance and exit points. 

Now take something like Citate Di Ravello from Just Cause. You can walk into the city from any direction, you can hookshot in, you can fly in if you find a vehicle, if you can drive in if you have a car. There aren't any strict entrance or exit points that you have to use if you want to enter the city. This is applicable for just about every single area in the entire game. Yes, some parts of the world are initially locked off, but the world itself is actually, well, a world, rather than a bunch of sectioned off areas with interconnecting passages (which isn't meant as a negative; I've thoroughly enjoyed the Souls' series). That's the difference between a standard exploration game and an open world game.

Perhaps more to the point, go look up just any gaming website's list of best open world games. You won't find Dark Souls, or Metroid, or Castlevania, or Zelda on there, despite games like Super Metroid, Metroid Prime, Symphony of the Night, and Ocarina of Time constantly being praised as some of the greatest games of all time. And that's not because the people making the open world lists just don't like those games as much, it's because the vast majority of the gaming press doesn't consider titles like Metroid or Dark Souls to be open world.

And, uh, no, Sexy Premium Beach Resort is most definitely not an open world game, even by the very loosest definition of the term. Truth be told, I'm not really sure what it is. Here's some example gameplay to give you an idea.

Over 35 years of gaming as well, but I don't think Witcher 3 deserves the top spot, not by a long shot. There are some great stuff in it, but as an open world it fails on so many accounts, and even in RPG genre there are at least half a dozen titles better then it (as open-world games).

I'm not surprised though, a lot of mainstream gamers played it and like it, but if we're being honest, game would be better if it sticked to TW2 formula instead of going open-world.