Fun, easy read. The visual layout of the text is excellent. Having virtually no familiarity with the specific subject on my way in, I do get the sense that it covers the fundamentals. The author appears to know his history, writes succinctly and with authority but is simultaneously very approachable, and doesn't dance around anything -- If he doesn't know something, he says it outright.
All that said, though, it ultimately feels more like a good coffee table book than some kind of reference book for Kaibyo (which admittedly is probably beyond what it's trying or claiming to be).
I would have loved a bibliography or to be pointed more directly to further reading ideas, although I'm happy it references select sources within the body of the text. The organization is clear but sometimes the excerpts don't cleanly tie back to what was just explained, so although not a pervasive problem by any measure, some stories lack context.
It's also not clear where some of the excerpts come from (particularly those that start the chapters) and it's my impression they may be the author's invention -- which can be fine to get the right sense across to the reader and introduce an idea, but since this book is specifically about Japanese folklore (and presenting as an authority on Kaibyo), I wish it was made clear whether anything was created, and if so: what was original; how much was derived but written in the author's own words; and why it was included as it was. Without that clarity, there is some danger in how these bits might be interpreted by readers present and future (i.e., as specific examples of Japanese folklore when they may more accurately be interpretive representations or suggestions of it).
Despite this criticism, overall I enjoyed the book, I definitely learned something, and I will read more from this author.