Far better than those who haven't seen it assume. The only jarring element is the witch, who in her mannerisms and the special effects surrounding her, seems out of place in what is a very well put together, traditional tale of loyalty and courage.
The samurai, the feudal Japan setting, even the body language of the cast, is spot on for the Era in which it is set.
Had this been told as a straight version of the Japanese legend, I have no doubt it would have been better received. Look past the special effects to appreciate this film for what it truly is- an expression of loyalty by 47 warriors for their betrayed lord.