This book excels by not just re-hashing the technical details of the M4 versus it's opponents, but by providing much invaluable 'soft' information that was every bit as important -- and perhaps more so -- than the technical details.
The author provides background information on how the Sherman was created and how the design changed - or did not change - over time. Shortcomings of both the Sherman and the Panther are covered in some depth. The author also touches on bureaucratic issues, metallurgy, training, crew experience, reliability (and the causes for reliability issues), availability of spares, ammunition, mission of the tank (tank versus tank, infantry support), the focus on the US Tank Destroyer concept, and many, many other relevant and interesting issues.
A large part of the book contrasts the Sherman against the German Panther. When you look at only the technical specifications, the Panther appears to be a vastly superior weapon to the Sherman. However, the book looks into detail at issues that exacerbated the Panther's problems, blunting it's technical edge, and the things that mitigated the Sherman's shortcomings, and made it 'work' better than the specifications would otherwise indicate.
While I consider myself very knowledgeable on WWII armor, I learned a great deal from this book. If you want to learn more about some of the 'soft' -- but very important -- issues that affect armor performance beyond the technical specifications, I feel that money spent on this book is money well spent.