Complex sentence: While not reaching great heights in critical or financial success, Ninja High School is one of few successful, long running manga-styled comics produced in America, and has contributed greatly to their continuing saturation of the American comics market.
Split into simpler sentences: While not reaching great heights in critical or financial success, "Ninja High School" is one of few successful, long running manga-styled comics produced in America. It has contributed greatly to their continuing saturation of the American comics market.