I actually am enjoying the game and find it a fun and innovative spin on MGSV's gameplay and mechanics, as well as a spin off of the original canon.
A lot of people say the storyline is bad, the zombie survival situation, and other tropes are overdone, but honestly, have anyone of these people really played the game for more than a few hours?
If you try to shoehorn it into canon, yes the game doesn't fit exactly, and the storyline is a bit wonky, but overall the gameplay is fairly solid. The survival system requiring you to hunt, gather, and craft from literally nothing is actually innovative and welcoming. You have to learn resource management, how to use stealth and more silent weapons to engage enemies, learn to use distractions, and learn to use a limited inventory.
It has a lot of features MGSV would really benefit from, if it had them that were present in MGS3, but more refined.
Once you get past the storyline, and get over the MGS lack of Big Boss, yet again, honestly the game does stand up fairly well. It's not perfect, but don't let the bad reviews on Steam speak for it. Play it for yourself.