Len Deighton does an excellent job in looking at nearly all aspects of the Second World War. One of its strongpoint is that he provides a lot of background in addressing the problems and events of the Second World War. In order to understand why the Battle of France was fought the way it was, he takes you back to the First World War, the lessons "learned," and events in the various armies between the war. To shed light on the Battle of Britain and the Blitz, he brings you the bombings of London in WWI, and what was thought of that at the time. In many cases, in order to understand why generals and admirals commanded their troops to do certain things, and why certain types of equipment were or were not available, you had to understand the mind set of the time, and the history they were drawing upon.
Another strength of the book is its look at the personalities of the people involved, which as much as anything else helped determine who won or lost. From Churchill to Rommel to Zhukov, you have to understand to an extent their personal motivations, how they interacted with their subordinates and superiors, and the lessons they had learned earlier in life. Churchill for instance was shaped by early life experiences in Cuba prior to the Spanish-American War and during the Boer War, and by his serving as the civilian head of the Royal Navy.
The book is pretty harsh on the British. While clearly liking the British (he is British himself), and greatly impressed by the courage of many of her warriors, again and again he lays into them for shortsightedness, petty infighting, turf wars, and failure to learn from battle.
All and all a good book. Less good for an overall history of the war, but better to understand some of the background of the war, some of the personalites involved, and why the two sides did not do better than they did.