This was one of the books that helped me to become a decent rock/blues player a year or two after I started playing. I'd give it a 5 except that it has no tablature (standard notation only) and perhaps might pale in comparison to the "note-for-note" Clapton transcription books out there. You can decide for yourself.
The main thing is that it has a section for Clapton solos and I used it to learn "Lay Down Sally" and a host of solos off the Layla album. Some are easy, some are hard, but sitting down with the records and this book really helped my playing.
This book also covers a fair amount of Clapton history and has a great family tree, linking Clapton to just about every British band from the 60's and early 70's (Zeppelin, the Who, Traffic, etc). Very informative.