The open world definitely seems very divisive. I'm enjoying it more now that I'm further in, but I still feel as a whole it's a bit amateurish and "off". I think even with the way it's laid out they could have done a lot more with it. It's really just one big sandboxish environment which only becomes interesting and relevant when you've triggered a mission or side op and thus limited your actual play space. When you're in these "zones" it's fun, as you're suddenly focused on moving towards an objective or whatever. But without that focus it's pretty damn boring.
It's technically "open world", but I think in overall design it doesn't play much like one, and instead is best played as structured missions and objectives that happen to take place within an "open world". For most part it doesn't feel like the game was actually designed around the landmass entire. If they wanted to aim for that idea they needed to make the design more emergent and dynamic, the ebb and flow of Afghanistan changing, forcing you to adapt and stay responsive to unique set pieces while exploring (that and actually having content worth exploring).
The Far Cry 2 comparisons are definitely apt, but even Far Cry 2 I think played better as an open world thanks to its stricter economy.
I really really like that MGSV's "open world" isn't actually an open world. Most games that attempt to do Open World end up shallow messes because they try to stretch content across some pretty mountains that occupy a needlessly huge continent.
I think for me it's just about balance. I'm so picky with open worlds, and I don't necessarily need them to be filled with content. Witcher 3 is a great example of an open world that, to me, gets almost everything right in terms of having a nice balance of interesting, discoverable content and also a ton of detail in scenery and presentation. It's stupidly huge, but it only took seconds for me to get completely lost and absorbed in the world they created. Meanwhile GTAV managed to accomplish the latter for me, the world acting like a giant 3D interactive space with absurd detail and believability, yet lacked interesting content to keep me hooked.
And I think that's the heart of my issues with MGSV's open world. It isn't built around emergent or changing scenarios, so exploring is always the same. There's little-to-no interesting or gameplay valuable content to discover outside of missions with the exception of grinding, reducing the value of exploration. Visually Afghanistan is extremely drab and (at least to me) repetitive and not particularly believable, the obvious level design bottlenecks for gameplay and hiding streaming painfully obvious, and also making long stretches of travel a bit of a chore as what looks like a logical path is in fact the exact opposite, forcing you to take the exhausting long way around. It's an open world that, outside of specific missions and tasks, fails to justify its existence. Which is fine if you're into that thing, or get into a rhythm of just kinda ignoring the open world aspect (as I am now), but does strike me as a little odd.
It's like MGSV is a game not built for open world that just so happens to take place in an open world.