I have almost 100 different plant identification guides alone; some quite specialized (such as the ones I have on lichens, mycology, or marine algae), and others more general, and this is probably the best general guide organized by region that I have. I like it even better than the Audubon Society Pacific Coast guide, or their Forests, Western Region, Guide, which are also useful books, but as they cover both animals and plants, of course the coverage can't be as complete on the plants as this book is.
The nature photography in these books just gets better over the years, and this book is no exception. The photos are truly excellent, and the identification notes in books like these have also improved substantially over the years. This book is no exception. I was formally trained in botany and plant taxonomy for a while, almost completing a master's degree in the subject once, and I feel I know a good plant guide when I see it, and this is a fine book.
Unless you want to get into truly professional-level plant taxonomies, which would usually require separate books on trees, flowers, lichens, etc., not to mention the greater technical knowlege required, I think this is the best overall identification guide around. It can't cover everything, of course, but it covers the most important and most common species. Overall, this is a quality guide and a great book to take with you on trips, hikes, outings, or whatever.