Believe me, I really tried to appreciate this book as either a thought-provoking exploration of scenarios of alternate history, or as a solid study of the art of history itself. I was disappointed both ways. Strangely enough, this book is purported by the publisher and editor to be both of those things, but the results prove otherwise. This book is very unfocused and academically arrogant, and it barely even explores counterfactual history, except at an extremely basic and dry interpretation of the term. Note: This book is from England and is quite Anglo-centric, so a working knowledge of British history might be an asset before you begin (this is not a criticism, just a recommendation).
This book gets off to a horrendous start with Ferguson's 90-page introduction in which he attempts to explore the nuances and importance of counterfactual history. Instead he delivers an extremely tedious and repetitive treatise on the study of history itself, which has little to do with the supposed focus of the book. A large portion of this intro is dedicated to "determinism" vs. "predestination" in history, but this is historiography rather than an exploration of counterfactuals. This is also written in that dry and verbose academic style in which it is more important to endlessly pile on repetitive evidence in order to impress one's colleagues, than to actually enlighten the reader. Ferguson shows a sheer desperation to confound other historians who don't think highly of counterfactuals, and in the process forgets that he is writing a book for the public. He also complains about researchers in his field not being taken seriously, but then insults people in other fields who are interested in counterfactuals, such as sociologists and fiction writers.
After this tedious start, the book doesn't get much better, as various historians contribute chapters on key episodes in history. With only a few exceptions, each author commits the errors of the introduction by failing to explore counterfactuals, which is supposed to be the point, and merely shows off his own historical knowledge in tedious ways. One noteworthy exception is the essay on home rule in Northern Ireland. Otherwise, the pattern here is to spend 95% of the essay describing what really happened in a straight historical fashion, then briefly knock off a few possible alternative scenarios without really exploring them, as if the editor forced each author to do this. In the end, this book can't figure out what it wants to be, and you will be unable to figure out why you're reading it. Is it trying to comment on the study of history itself, or present straight history with an intellectual twist, or explore counterfactuals? It tries to do all of these, with disappointing levels of success, and is only unfocused as a result. If you decide to tackle this, good luck - you'll need it.