Having only recently discovered the story of Miyamoto Musashi, I have watched as many versions as I possibly can. The 49 one-hour episodes that NHK produced during 2003 is by far the most comprehensive effort to re-telling the Musashi tale, as influenced by the book "Musashi" by Yoshikawa Eiji.
Overall, the development of Musashi as a wild man into a well-developed martial artist is done very well. The plot develops well and the cast really does a superb job, and not just the principal characters but the minor ones as well. The fight scenes are also very well-done and most are better than the movie versions from the 1950s and 1960s. The suspense in the lead up to the duel at Ganryujima was well worth it.
The only downside I did not like was that the story continued after episode 38 - the duel at Ganryujima - for 10 more episodes, which really focused more on the battle between the Tokugawa and Toyotomi forces, with Musashi's story as a sideline. If you are big on purely following Yoshikawa's book to the series, stop watching after 38 or 39.
The other development I was not too fond of was the "magic" and mystical elements that was supported by two magicians who are in the series. I wish the script was more true to life (if such a thing is possible when discussing elements of a character like Musashi that already has too few accurate historical documents attached) rather than going a bit out of the box occasionally with disappearing characters and other magical elements.
Overall, however, they do not detract from the superb production NHK made. They should be applauded for their efforts and anyone truly interested in Musashi should invest in watching this series. The musical score by Ennio Morricone is also absolutely amazing and epic as it is employed throughout the production perfectly. 9 out of 10.
Also recommended: the Musashi 5-part series with Kinnosuke Nakamura
