There's too much plot. It crushes all the other aspects of the film. Much of the dialog sounds, in translation anyway, like a collection of aphorisms taken from some Bushidō "Words to Live By". I imagine that this is a translation problem since Shinobu Hashimoto has proven his prowess elsewhere. The acting highlight for me was seeing Yûnosuke Itô do an ace job playing a shifty-eyed mouth-breathing henchman.
The film's original title, "Samurai" is so much more potent and poignant than the generic and kitschy "Samurai Assassin." This is my third Okamoto, after "Sword of Doom" and "Kill!" It fits comfortably somewhere between those two, offering a cynical and compassionate interpretation of Japanese history, jidaigeki, and contemporary cinema.