I love the Lone Wolf & Cub series and even though this movie is just cut together its still good.
The atmosphere in the movie is authentic. Costumes, weapons, language (according to a japaese friend) are all well done. And combat action is just awesome. Limbs flying, blood splashing and heads being cut off - this is swordfighting at its finest.
I probably watched the movie 4-5 times already and enjoy it every single time.
Story-wise its certainly not as deep as the Lone Wolf & Cub series but still provides good entertainment and a welcome introduction to the world of Shogun assassin.

Do not bother seeing Shogun Assassin at all.
Try to get your hands on the six Lone Wolf films instead.
If you're only interested in the orgy of blood and sword fights, watch Kill Bill 1.

Shogun Assassin was banned in the 1980's for the level of gore it contained. I think that the censors were too harsh in their treatment of the film. This is a solid samurai story of vengence and the tale of a father and son's journy of revenge. There is plenty of action and lots of gore, but it still tells a touching story, worth seeing.