This is an interesting little book. It was written by Miyamoto Musashi who was not a samurai for most or all of his career in the proper meaning of the term. Instead he was a duelist who never lost a battle and this was in a period when most duels were to the death. Musashi's book is very much a practical guide to killing with a sword. Even less than the Art of War does it have an application outside of the martial arts. It is therefore primarily of interest as a historical document. What I think is most interesting about it is the extreme practicality of the method. Musashi poo-poos anything that would smack of a Hollywood or Hong-Kong fight scene. Musashi is not a great writer and will sometimes say that what he is trying to communicate cannot be communicated in a book. He often also says that one needs to reflect upon a particular sentence to understand it and this reflection is meant to take years. However, there is a certain charm to the work, if charm is the right word for a book so totally focused on killing. I also have a deep love of Samurai movies and certainly many of the people who have made those movies have read this book.
The Book of Five Rings is a very slight book and my edition also includes The Book of Family Traditions on the Art of War by Yagyu Munenori. Yagyu was in a completely different position than Musashi and was a very important person, basically the Shogun's personal bodyguard and by all accounts an effective swordsman as well. The book was written within a few decades of Five Rings, but does not quite have the same charm. The influence of Zen Buddhism is more developed in this work, but I am not sure how well Buddhism and martial techniques go together, so the greater emphasis on Buddhism is less effective. Somehow the work is not as fascinating, but it does have historical interest as well.
I found both books to be well worth reading, but I am utterly fascinated with this period in Japanese history. I am not sure that the books would be as interesting to someone who was not interested in either Japanese history or the mechanics of swordplay, but for anyone with either of those interests they are must reads.