Amazing book. The first act is a fantastic set of tableaus about the physicists and progression of science necessary to discover the capabilities of the atom. The second act is somewhat dry, regarding mostly the politicking necessary to have made the bomb happen, but there is some decent engineering spliced in here and there. The third is about the war effort, the Trinity test, and the eventual dropping of the bomb. The last chapter is horrifying and not something I'd describe as the feel-good read of the year, but it helps to drive home just how terrible these things are.
I would strongly recommend this book to everyone.