Nobunaga Shiki is one of many great books written by historian/novelist Tsumoto Yo. If you have read is best selling novel on Nobunaga Genten wa Yume ka, then this book is also a must. The ten chapters explain Nobunaga's make up, guns, tactics, intelligence, leadership, ladies, economics, Honganji, the Honnoji Incident, and Nobunaga's dreams.
I have both hardcover and paperback. The paperback edition includes a couple pages written by Owada Tetsuo, a major bonus.