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.
Ground Zeroes and the trailers for V made me think Kojima had gotten his shit back together after 4. I was sorely sorely mistaken. Having big boss be the protagonist in anything but 3 was a mistake and Aldo the series should have ended with 3. Story wise anything after does nothing but ruin it.