Up to now the orthodox approach has been that the German Army devoted all its efforts to the creation of "Blitzkreig" offensive war. But as this book points out, in fact the German Army spent most of its time concentrating on defence. This alone would make this book a ground breaking one and it should be on the bookshelf of any any self respecting historian. It gives a comprehensive account of the development of doctrine and tactics and war plans throughout the inter-war period and provides details of their origin in the Great War and their success of failure in World War Two.
However this excellent account is marred by a couple of points. The author has taken his information for the Great War from a source that although commonly used, has many flaws in it, so there does not appear to be much in the way of original research in this area. The dynamics of doctrine: The changes in German tactical doctrine during the First World War (Leavenworth papers)
He would have done better to provide his own assessment of the period and to have drawn on the excellent, though flawed, Wynne papers If Germany Attacks: The Battle in Depth in the West (West Point Military Library)
especially the new 2010 edition. It appears that instead of the single tactic proposed by Lupfer, there were two tactics as outlined by Wynne and this would explain much of the thinking in the time of the Reichswehr and subsequently.
Likewise the chapter on the Second World War is a bit of an after thought and does not really cover how well these inter-war theories got on in practice.
Having said all this, this is a really ground breaking book that is well worth reading if you are interested in the development of the doctrine of the German Army