I have the 2011 edition of this book. It is very good reading for the intermediate gardener. The bulk of the book is an extensive, A to Z encyclopedia of perennials.130 genera are described, with color photographs of various species or prized cultivars. There are one to six photos per page, adding up to a gorgeous book. Armitage gives each species a personality, and shares the nuances of one versus another. There are some lists of plants for special situations at the end (aggressive plants, cut flowers, etc) to help narrow your choices a bit.
This would not be a book for a beginner; it assumes you have a basic general understanding of gardening. It's an enjoyable book for any gardener who wants to see what else is out there and be tempted yet again to buy more plants!