I was unfamiliar with the story behind The Three Treasures and the legendary founding of Japan and Shintoism, and I found the film hard to follow, overly long, and ultimately a bit boring (even the fight between Susanoo (the great Toshiro Mifune) and the eight-headed dragon). Some of the imagery and special effects (from Toho Studios master Eiji Tsuburaya) were very good and the acting fine (for an action-fantasy film). Mifune is fine in the dual role of Prince Yamato Takeru and Susanoo, although I found the Prince's constant credulousness tiring (he is repeatedly lied to yet seems to believe everything he's told). I think I'd need more background in Japanese history and culture to really appreciate this film (fortunately not required to enjoy Toho's rollicking kaiju epics).
Review of The Three Treasures
