Nauseating is indeed the term. I kind of wonder how engaged Faber is with SF, because its clearly an SF novel, but kind of one you'd expect from a literary writer, maybe? Theres both a lack of the orienting genre touchstones, which could be done on purpose, but theres also a kind of stretched out didactism that just belabours and belabours the point. We get it, its a metaphor. Like, i've read punchier short stories of this conceit, but I can't imagine it being spun out into an actual genre novel - too hackneyed. I recognized the issue (too easily and too obviously, perhaps) and then put it aside, because it wasn't really making me think anything new or complicated about it after a while. A good moral-instruction sort of SF novel usually more layered, and throws a lot more themes, issues and impressions at you with more nuance and complexity, and forces you to wrestle with them yourself.
That aside, its not a bad book. It works particularly well as a character piece, and theres a nice mystery-horror atmosphere to the first part, and as a hitchhiker, I sympathize with that queasy 'well, awkward now. Are you going to make my skin into a hat or are we going to talk about your kids?' feeling. It's just too long, I suppose.