This title is really only the first part of a three-part story of the early life of Musashi, the legendary Samurai. The three parts were released separately and Criterion DVD has released them on three separate discs, each disc about an hour and a half to two hours long. You can try to watch the first disc alone, it stand by itself, but it ends just as Mushashi starts out on his quest, and you'll miss Koji Tsuruta's serene and slightly creepy role as Kojiru, Musashi's arch-enemy, which for me was the best part of parts 2 and 3.
The DVDs feature not very well restored prints, maybe it was the best they could do, and there is no supplemental material.
The movie itself is a fun and lively retelling of the legend. Mifune is more wooden than usual, but this is a time when Japanese action films were taking their cues from westerns, and his Musashi grows from a wild spirit to the requisite strong, silent type. For a modern, charismatic, manga-style Musashi, try to get your hands on 2003's "Musashi" NHK miniseries.