Reason for recommendation:
Best overall single-authored instructional origami book I have seen, judging by the quality of designs, folding sequences, diagramming, etc.
No, I'm not saying that I've seen a lot of instructional books (definitely not as much as those book collectors at least), but it's hard to imagine an even better book than this one.
Instructional books are meant to let people enjoy practicing origami, and there are several factors that determine how enjoyable they are.
The first thing is the quality of the designs themselves, and that also breaks down to several factors. Are the models aesthetically pleasing? They surely are. Is the idea behind those designs novel and inspiring? Definitely yes, most notably as Kato made famous his "tilted grid system" through various applications in this book, which has since inspired many new designs by other origami artists. Do the models provide enough challenges for enthusiastic folders? Certainly, many models in this book are among the highest complexity of all sequentializable designs.
The second thing is the quality of the folding sequences, and this is perhaps the most impressive part of this book. Many designs in this book are typically considered not sequentializable, but Kato managed to sequentialize them nevertheless, and his folding sequences are considerably fair to follow. I would say he has pushed the boundary of sequentializability.
Finally, we have the quality of diagrams and other ingredients in the book. Kato's diagrams are textbook examples of what good diagrams are about: clean lines, just the right amount of offsetting of edges, good use of shading, and amazingly well-drawn 3D steps. Especially after I've done my first set of diagrams earlier this year I am astonished by the time and effort he must have put into this book. He also incorporated many of the best elements to make this book excellent: recommended sheet sizes, the relative sizes of finished models, beautiful photos of finished models, and the silhouette indices near the corners. Kato's book is no doubt a role model for all origami authors.