A lot of information in here about projects that didn't happen. Of particular interest is the section on the X-20 DynaSoar. There are some interesting insights into Robert Macnamara and his obsession with ICBMs, which lead to the demise amongst other things of the B-70 and the F-108.
Also a very good section on the Canadair CF-105. For British readers, there is a section on the TSR-2 although there is little new here that hasn't been already published elsewhere.
In keeping with the 'what -if' theme of the book, there is some excellent speculative original artwork from the author (e.g. of a CF-105, TSR-2 and B70 flying in formation) and some period photography.