Ninja Gaiden II is one of the bloodiest action games ever made. Because of a design decision we may never understand or forgive, Ninja Gaiden Sigma 2 is, by comparison, nearly bloodless. It takes the viscera out of all the evisceration. The action is as intense as ever, but I can't honestly say it's quite as satisfying. Every dismemberment and decapitation is accompanied by a jet of flame and a very small spatter of blood. I guess that's supposed to represent the evil that has infested the bodies of all the Fiends and Black Spider clansmen, but I'm not buying it. Violence aside, Sigma 2 is a better-looking version of Ninja Gaiden II. Some of the environments are still a bit on the bland side, but it's okay, since your eyes will be focused mainly on the outstanding character designs and animations.
You have the option of using either the English or Japanese voice track, and I strongly recommend going with the Japanese track. The voicework for the English track is pretty bad, even when taking into account that the dialogue is beyond redemption. Plus, if you use the Japanese track, every extremely powerful attack is announced with a savage "HWAAAAGH!" instead of a "Ya!" or a "Hoooh!" The music is decent, as well. It won't send you into a bloodthirsty rage like it probably should, but it's nothing you'll hear in an elevator.