Sigma 2 is a superior game compared to 2. You should play it.
I have played it.
How is it superior?
Did you see what they did to the magic attacks in Sigma 2? They were all turned into cutscenes like an RPG for some reason. They removed some of the areas and replaced them with more back tracking sections that added nothing to the experience besides making it longer. They changed the story to add more Dead or Alive characters, but it ruins the barely logical canon of both series because almost none of them met then.
They also took a series based on the story of one person and added three female characters to part of the story that add nothing to the experience, two of which are not even featured or hinted at in the original game, meanwhile Sonia is not playable even though she would has different kinds of weapons. It is like being able to play as Joy, Xiuying and Ine-san in Shenmue 1, it is stupid and makes no sense. They removed and replaced some other stuff, but I cannot remember anymore. Ninja Gaiden II had a lot of flaws, but Sigma 2 was in no way superior. They even made the story more serious, WTF