Well, to start with, this book is not particularly 'little' - measuring approximately 15cm square - nor does it exclusively feature gargoyles, and it is definitely not comprehensive (nor does it pretend to be).
All that said, it is lots of fun for anyone remotely interested in the weird and wonderful carvings and paintings that adorn the churches of the UK and elsewhere. The book is basically a collection of the author's own photographs, together with comments and some home-spun philosophy on the meanings of each item or category.
The pictures are excellent - you'd think they were taken by a professional photographer specially commissioned for the book, rather than an eternally-touring 'comedian' and cohort of Jasper Carrott. The text is middling. But then, anyone buying this book is probably not looking for profound insight - I guess purchasers of this book will probably be people who already have an interest in the subject, looking for something other than dry academic analysis, or people expecting a collection of weird pictures, or people with a passing interest who don't really want to dig deeper. All these types will be satisfied by what is really just a fun book, but one which encourages people to look a little bit more closely on their next visit to a church or cathedral.