He brought a continuity of humanity to the "superhuman" archetype that was born in the 1930s.  He had such an abundance of power but what was on his mind was saving people.  He had altruistic and other human kindness traits that other superheroes either didn't have or couldn't find because of their psychological problems. Audiences loved the Flash - time and again, it brought DC Comics the fans and financial gains during times that we're seeing lower comic book popularity.