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I have no doubt that Greenfield could write brilliant, well researched and insightful essays about each of his central premises. Unfortunately, for whatever reason, he decided to explore those ideas in novella length fiction that reads very much like essays forced into a story format.
One of the basic rules of good story telling is to show rather than tell and this is where Greenfield fails. The stories are 90-95% exposition. Each story even has at least one section with bullet points.
The majority of the stories are made up of dense blocks of prose with very little dialog. According to the section at the end of the book, much of the dialog is taken directly from something the person actually said. A large portion of what little dialog exists consists of political speeches or winks to the reader about how events actually played out or things that will happen in the future. For example, in the first story which has the premise of JFK being killed by an assassin before his inaugurating LBJ comments at least it wasn't in Texas and either he or another character expresses gratitude that the assassin left a clear motive or there might be all kinds of conspiracy theories. In the second story a young Roger Ailes says something along the lines of "someday maybe there will be a fair and balanced source of news." And in the third story someone says of Reagan's surprise (female) nominee for VP that "at least she'll know how to answer what she reads." I found the winks to the reader irritating but your mileage my vary.
The other thing I found irritating was that at least once in each story he felt it necessary to remind the reader that the Internet either didn't exist or didn't exist as we know it when the stories took place and the flow of information was more tightly controlled. I'm pretty sure anyone who has read to that point has a strong interest in history and/or politics and doesn't need to be told that the Internet wasn't a factor in the 1960s.
The premise of each story is intriguing, especially because of how plausible they are. But for a small twist of fate, each could have easily happened. Greenfield does an excellent job not only demonstrating what small thing would have to be changed but exploring the enormous ramifications of such a change.
If you have a casual interest in alternate history fiction you'd probably be better served by something else. But if you have a strong interest in history and politics, particularly if you have an interest in the Kennedys, this is worth checking out.