I prefer science fiction, fantasy, and horror without the spaceships, dragons, and zombies.
This novella is about the right length to explore a schizophrenic man's fixations, obsessions, hallucinations, and his inability to cope with the real world we all share or the nightmare world that exists only (presumably) inside his head. We're also presented with some glimpses of the early childhood origins of the symbols and themes that inhabit this man's hellish world.
And the book doesn't go much beyond what I've relayed above. Does it need to? No, I don't think so. To me, it seems that the point of the book was to construct an artist's representation of a schizophrenic man's internal life.
Can I know if this was successful? No.
Was I adequately convinced? Yes.
If you're not put off by what I've written above, I'd say give it a go. The prose is lean, almost minimalist, which is nice considering that this particular type of book could easily get weighed down with dense stream of consciousness passages and endless descriptions of hallucinations.
Saunders, thankfully, does not outstay his welcome.