It's an excellent academic book. I'll take it a step further, I did not know the significance of learning scales (pentatonic, major, and the accompanying chromatic scales). Desi advocates the importance of learning (covering songs..right?) well, I've taken it so much further.
My style (new age, space rock), I'm composing these days thanks to this book. I'm an academic kind of person; been searching for an avenue that could show me guitar academics in such way that I could relate better than just ordinary guitar lesson the last eight years. I have tinkered with all the songs Desi advocates learning and as mentioned, when you master the scales, your brain will kick in and that's what has happened to me.
If you purchase this book, be assured, it will help you beyond reproach. I have other books from famous people. Desi is an excellent technical writer. He knows his stuff and presents it well. Get it!
Desi, (ya happy now?)