The actual execution was a mess, but Skullface's inspiration for his parasite weapon being the experience of linguistic imperialism as a child was a really novel premise. The idea that he would get his revenge by creating a weapon that killed anyone who spoke English is some cool super-villain shit I don't think I've ever encountered before. "Race-selective" weapons, genetic-targetting weapons, religious indoctrination viruses, I've seen all those, but I think MGSV is the only time I've encountered a weapon that targets a language community.
Death standing was really good, sure it was weird but it ultimately was an exploration of modern alienation and the breakdown of social structures with some decent side themes relating to mortality and social reproduction.
Maybe I’m just biased it managed to make walking an interesting mechanic.