Boy oh boy, where to start.
First off, the game is literally a scam. It deliberately decieves the player. Now, some of it is obviously completely intentional (take a certain menu at the very beginning with the doctor, you know what I mean), some of it the game tries to hide desperately, like numerous times where this "open-world, NON-LINEAR" game actively forces you to do certain things exactly the way the devs want.
Make no mistake, this is NOT an open world game - it only creates the illusion of the open world. The exploration value aside from gathering a few scattered resources here and there is literally non-existent. You just go from camp to camp and that's literally all the free-roaming freedom the game grants you.
The menus are cramped with infoboxes, buttons and numerical values to the point where it's literally "oh **** it's Eve Online all over again". The management part of the game thus is just pure hellish torture unless you're a big fan of your screen being full of numbers and letterboxes.
The controls are somewhat counterintuitive - I've struggled for a few hours getting used to the traversal system, and I'm no noob. Get ready for quite a few awkward moments where you dive head-first onto the ground in a prone position when trying to jump. Did I mention there is no jumping in this game? Oh yes, you will NOT be able to climb anywhere where the devs don't want you to be, even if it makes perfect tactical sense.
Now, the fans of MGS franchise will probably expect it, but to all the newcomers out there - beware, this game is effing WEIRD, and not always in a good way. You'll find that the game utterly disrespects you as a player on numerous occasions. It can't even decide what it is - is it a stealth game with serious themes and issues and maybe a few fun easter eggs here and there, or is it a straight comedy ****-show riddled with things calling for some cheap laughs, especially when it's extremely counterintuitive and to the narrative and just feels off. Remember Mass Effect where there were some good laughs when the situation was appropriate? Forget about it - this "masterpiece" just loves to sell itself as a cheap 90's sitcom.
Know why they called it "The Phantom Pain"? Because you'll be constantly getting phantom pains from the things that you expected to find in this game but they're not there.
All in all, I'd recommend to avoid this game if you're not a die-hard fan of the series.