It blows genre out of the water for me. I could easily imagine it converted to fantasy. The few things that made it sci-fi and not fantasy were so peripheral. Probably could say that about plenty of Fantasy OR Sci-fi books. But the worldbuilding accomplished in such a compact story was just so insane that at the end and always in reflection that feels like the genre more than any other. Worldbuilding. And of course you could assume fantasy or sci fi would be foundational Ariadne's Thread for a genre called Worldbuilding but I also find it in John Dies at the End. For the purpose of the reading experience I am wondering why worldbuilding itself isn't part of genre tagging systems in GoodReads because it feels like a type of book even though, I assume, it has always been categorized as just a part of the writing process.