Being the first thing I've really read on the subject, I can only say so much about it. I felt it was a good overview of the history of documentary photography. The focus was on the importance of groups and individuals of the 30s and branched out from there. Personally, I mostly enjoyed the quotes from the photographers themselves that explained their approach and personal philosophy.
This is not a HOW TO book. There is a short chapter on methods and techniques at the end, but it seems to have been put there to satisfy expectations rather than necessity. What Rothstein offers is a look at the life of documentary photography so far and the people who've been a part of it. By looking at their work in context and hearing them speak, this book is far more inspiring.