As he notes, there are a bazillion books on Churchill – why do we need another one? The idea here is that a book could be written that focused on Churchill as a war leader – what did he do, and are the many stories about the inadequacies of his war leadership true?
Again, the twin problems of reading a book on the Kindle, which renders it indistinguishable from many other books I'm reading or listening to at the same time, often on overlapping subjects, as well as trying to write a review months after I finished it makes it difficult to be specific about my impressions. But I can say this.
The book does provide informed insight into what Churchill does. Some was good, some was bad, but it's expert analysis from someone who's familiar with the subject matter and – important for an American reader – familiar with the British parliamentary system, so he can explain what's normal and what's not. He also explains the threats Churchill faced to his political leadership of Britain as the country went years without a military victory – something the history books generally don't bother with because they didn't amount to anything until late in the war. Churchill was never playing with a strong hand, and his greatness was that he bluffed shamelessly in defense of freedom when no one else would.
The problem with the book is its narrow subject. Once the U.S. become the dominant partner in the war, there's not much to tell, and the book has the sound of a giant sucking straw. Churchill was reduced to pleading with FDR to do this or that, and FDR was, while polite, largely immovable on matters of military strategy as developed by the combined chiefs, and more particularly by the U.S. chiefs of staff. So Churchill was the leader of a nation which no longer controlled the strategy of the war. That's a story, but an increasingly uninteresting one – except for the fact that when it's Winston Churchill it's never uninteresting!