It's good.
I used it as the textbook for a class I taught at Indiana State University last semester called Survey of American Popular Music Traditions.
Campbell did an excellent job of tying together early sources of early American Popular Music from the outset - after he defined popular music at the beginning of the book.
I would like to have seen a bit more coverage of three popular acts: Sister Rosetta Tharpe, T-Bone Walker, and Crosby, Stills, and Nash. Tharpe is conspicuously absent from this book, and Walker is mentioned maybe once or twice in passing, but these two were hugely influential on such key figures as Chuck Berry and Elvis Presley - among many others.
The influence of Crosby, Stills, and Nash on the folk rock sounds of the early and mid-70s cannot be overstated. The Eagles, America, Seals and Crofts and countless other popular groups were directly influenced by CSN - big time.
Overall, a very good work.