Niccolo Machiavelli's 'Art of war' has been one of the most pleasurable reads of late. He seems to cover everything you can conceive using the Roman army as a template of excellence, and why not, he manages to cover a broad range without going in to boring minutaie details.
Written in the form of dialogue you really get the feel of being instructed in the art of warfare, without being patronised or treat as though you are clueless about such things. Throughout Machiavelli gives his opinions on various tactics and methods and supports his opinions with good evidence that this would be the wisest course of action.
The book is divided in to two sections, the first would be of great interest to a military historian or anyone with interest in the Ancient to Renaissance age. Again using the Roman army as a template of military excellence he covers the historic detail beautifully, like an artisan storyteller.
The second part of the book would be well sought by someone interested in military tactics, how to use cavalry, infantry, artillery, in fact anything you need to know about a decisive victory, such as a war should be won through food, or lack thereof, rather than steel. Starve the enemy and protect your troops at all costs is order of the day, among other tactics.
It is true many military historians have attacked his work, some on a point by point basis, but for me this work stands up against their criticisms rather well and should be read and on the shelves of anyone interested in the art of warfare, no matter which period that may be.