Terrific post Night. Your thoughts come across as very honest and insightful.
I think the only portion I didn't fully understand was this bit:
I haven't played Hitman or Thief, but are you citing MGSV because of the sandbox nature of the actual gameplay, or because you can complete missions in a non-specific order?
Where would you say something like Fallout lies in that spectrum?
I think Nightengale means that games like MGSV and Hitman have "open worlds" designed as a sandbox to give players various ways to complete a mission. The game essentially doesn't limit the player down a set path and the player can use equipments at their disposal to accomplish the objectives. Take Mission 16 in MGSV, for instance. You are given a large portion of the map to navigate in and your objective is to find the caravan, which is at the airport. The game encourages you to infiltrate a nearby outpost to gather intel to locate the caravan. However, if you're familiar with the layout, you can rush straight to the airport, defeat the Skulls and fulton the truck. You can even just use D Walker to fulton it from outside the base. If you're too slow, tanks arrive and escort the truck, in which you have to stop the caravan on any point of their route. Basically, the open world is designed to be fully open ended, giving the player freedom to finish the mission as they wish with collectibles being non existent, but side quests are included.
On the other hand, the other type of "open world" is one where you have an entire living, breathing world to explore and participate in. The main difference is that in free roam, you are encouraged to look around the world for collectibles and side quests. You can also simply indulge in this rich world, interact with NPC's and such. However, this type of games typically offer little freedom in mission structure, usually forcing players down a set path. GTA games and The Witcher 3 being good examples.
In my opinion, Ubisoft games should be in their own category. The worlds created are not fun nor interesting to explore at all. Their game design philosophy is to fill the map with repetitive side quests and bland collectibles. Hopefully, Horizon has open world design more akin to GTA and The Witcher.
Damn it, I see Nightengale replied. Oh, well, I hope I got it right anyway.