I'll always defend how good MGSV is, even in comparison to the others which were mostly great, with way better storytelling. But there's this consistent meme I keep seeing that 'we were promised to be shown how Big Boss goes evil, but we never got it we got Venom instead!' and I just gotta shake my head. Venom's existence as another clone of Big Boss, created by Big Boss himself is the crux of his villainy. To post a comment I made on reddit ages ago:

People be sleeping on the events of MGSV being the symbolic step for BigBoss towards being a villain: he quits the Patriots after learning about Les Enfants Terrible, thinking clones of himself to be abhorrent and horrible, basically stealing lives from real people to try and recreate the perfect soldier. Meanwhile, after BB almost dies in Ground Zeroes he has a heel turn and decides "two of me would be good, actually, my project is too important to fail" and thus Venom is born. Yet another clone of boss created by the boss himself, stealing that mans very identity from him to be replaced with Big Boss. The whole game has an unfortunately poorly explored theme of identity formation, what with skullface and his philosophies on language.

I really wish we got an actual ending for that game. The retail release has way too much dangling to be called finished, and the work in progress cutscenes of the true ending are only okay.