This 267 page encyclopedia may very well be the most thorough listing of hydrangea cultivars to date. It has almost 800 full color photographs of various species and cultivars and is written with an "english" sense of humor that I particularly enjoyed. It is an incredibly beautiful book, and very useful for identification of hydrangea cultivars, contains history of certain cultivars and breeders and in general is a very good reference book, that you might want to have on your shelf if you are a serious hydrangea enthusiast as I am.
I have been searching for a complete reference book for hydrangeas and I had hoped that this would be the one, however, while it is definitely the most thorough listing of known cultivars I have found thus far, it still does not cover all the aspects I am looking for. My biggest pet peeve with all the books I have purchased thus far, is that they ALL tend not to give specific zone or hardiness ratings for each cultivar - and hydrangeas can vary GREATLY in their hardiness. Unfortunately the authors of this book gloss over the hardiness and lump ALL hydrangeas together with an, "In general, hydrangeas can be grown successfully in U.S. Department of Agriculture Hardiness Zone 6,..." This does not help those of us with northern gardens in zone 4 & 5. We know there are hydrangeas for us, but this book will not tell you which ones. I frankly find that a bit lazy on the authors part, that they don't take the time to do a thorough listing. But the same was true in Michael A. Dirr's Hydrangeas for American Gardens as well.
Overall, because of the superb photography, humorous analogys, and very thorough listing of cultivars - including many of the lesser known ones, I give this book a positive rating and would recommend it to others.