This is an interesting concept: Attempt to explain the the life, thoughts and martial arts of Japan's most famous strategist/warrior by untangling the few historical facts we have about him, dispel the fictional and misleading account of him make famous in a novel by Eiji Yoshikawa and present it all with manga-type scene reconstructions narrated by the host of the documentary. The concept is very well executed, although some of the CGI is a bit jerky here and there, the narrative is very informative and the history and ideas about Musashi are compelling. But its the CGI host(and his short-skirted, bob-haired bimbo assistant) that spoils this title for me. In an attempt to make the whole thing a bit more humorous, the narrator is CGI-ed as a South Park-like character who, unnecessarily, trips over things, is squashed by his assistant who is constantly trying to dispatch him, Cato-style, and many other distracting silliness going on with them both for the duration of the documentary. It turns a potentially excellent adult documentary, presented in a new genre (manga) into an irritating, childish cartoon. Simply removing the images of the CGI narrator and assistant plus the associated sound effects would have elevated this to 4 stars if not more.
If you can get past this, probably though gritted teeth, then you will learn something new. If you get distracted by this kind of silliness, don't buy this!