This is definitely a five-star book in theory. It's probably the only Japanese cookbook that comes close to Shizuo Tsuji's in its thoroughness and completeness. But that's also the downfall of this book, it is really too similar to Japanese Cooking: A Simple Art without offering anything that breaks through the precedent. Those of us who own and cook from the previous book a lot might find this book a little bit boring. As soon as I got this book I thumbed through the pages and I only picked out 4 recipes at first blush that I really felt like I needed to try. This is a pretty good size book, too. I've cooked more than those 4 since then, but the book didn't have the profound impact on me that it should have, probably because I've read it all before in Japanese Cooking.
I will say though, that this book can offer some things that Japanese Cooking doesn't have, mainly photography. There are pictures not only of finished dishes but of ingredients too, and even though those are artistically well done they are also quite informative. It helps to know what something looks like when you're looking for it in a store, I would suppose. But there are some steps skipped in this book that Japanese Cooking doesn't overlook. A specific example is a couple days ago when I made an asparagus and black sesame salad from Washoku to go along with lunch. Earlier today I was just perusing Japanese Cooking when it mentioned to never use wet ingredients in an aemono. Oops, nothing was mentioned about that in Washoku. I checked and sure enough, my salad, which was perfectly nutty and crisp at lunch, was now sitting in a pool of gray asparagus water. It might have gone without mentioning because no one bothered to check how it would keep as a leftover, but Japanese Cooking mentioned it, which just shows a more complete understanding of the cuisine in that book.
I would say that either this book or Japanese Cooking would probably be the best basic Japanese cookbook out of all the ones out there. You certainly don't need both though. I would browse through both of them and see which format fits your style most. If you need visual stimulation and prefer coffee-table style books, then Washoku is your seminal book on Japanese food and cooking. If you value, on the other hand, a very in-depth informative, Julia Child-type approach and format, I would have to recommend sticking with Japanese Cooking: A Simple Art by Shizuo Tsuji.