Having played guitar for many years, I have to admit to having a great hole in my knowledge when it came to the fretboard. Sure, I learned stuff, by ear or by patterns, but I never really learned about the fretboard. Now that I've begun to learn it, I realise I am not alone.
This book is a masterclass.
What it is not - it is not really a playalong book in any sense of the word.
What it is, is a series of exercises that will really enable anyone who sticks with it to have a really good understanding of the fretboard on the guitar. However, it is much more than that, there's a wealth of music theory contained within it that goes way beyond the guitar. But it's subtle, simple in it's explanation, deep in terms of what it will give you in terms of understanding.
There are lots of exercises to do. All the answers are at the back for checking. It takes a bit of personal discipline to work at it, but by doing a bit at a time it doesn't become a chore and my all round knowledge and playing is improving.
Like others have said, there are a lot of disappointing books out there, this stands head and shoulders above most of them.