This book by no means settles the debate over whether or not it was wrong ethically or strategically for the United States to use atomic weapons (they had not yet graduated to being called nuclear weapons at this period) near the end of the war with Japan in 1945.
Frank's contribution draws heavily on facts and details known at the time -- to help render a judgement without benefit of hindsight. His research into military strengths and weaknesses, production capabilities, longer-range plans is thorough and far more engaging that one would normally think a presentation of large amounts of statistical data would be. His use of sources from both the Japanese and American sides, as well as his analysis of diplomatic versus military concerns and strategies is well done. His analysis of cabinet-level thinking on both sides deserves to be carefully studied, as it draws upon contemporary documents and, where those conflict with hindsight recollections, he lays the controversy bare and lets the readers decide for themselves. His analysis of the role of the emperor in particular deserves special consideration, for it neither paints Hirohito as a puppet or a warmonger, but as a human leader with internal and external considerations to weigh in decision making.
Frank begins with a description of the firebombing of Tokyo, a tactic in itself probably as horrific as an atomic blast, with similar resulting damage and casualty counts (remember, the early atomic weapons were quite a bit less powerful than todays models).
I would have welcomed more maps, in particular showing Japanese and American forces at the end of the war. Frank does have maps showing planned invasion routes of the southern islands, both from American contemporary intelligence and from a Japanese actual-strength perspective -- this difference alone is best seen in a side-by-side comparison; anyone who thinks American and Allied forces wouldn't have undertaken the worst battle in the history of the world to that point is deceiving themselves, and the casualty rates on both sides would have far exceeded the Hiroshima and Nagasaki totals.
A clear, detailed yet concise history of the final days of World War II.