For me, earlier versions of macOS/OS X and Windows Vista/7 were the right mix of eye candy and usability. Apple's just showing off with this liquid glass thing. Yeah, it's cool that they attempted it, but it should've remained entirely opt-in. Apple being Apple, there's no opt-in -- once they like it, it's the default.
For a major revamp, you should either do it or not do it. Making it opt-in or even opt-out means every app then has to try to support both different UIs, which is a longterm maintenance cost. Not only for Apple, but the entire ecosystem.
I personally sort of like the liquid glass, but it's also kind of a mess in a lot of edge cases. I feel like it was an interesting idea that didn't really pan out fully and should have been scrapped. It's just too controversial for pure eye-candy.
