He sang a lot of sad songs and led a very tragic life.
Every big success he had was followed by something tragic in his personal life.
He had an impressive 3-octave range and the audience loved him. Here's a qute from his bio:
A year before Beatlemania overtook the United States in 1964, the four lads from Liverpool invited Orbison to open for them on their English tour. On his first night, Orbison performed 14 encores before the Beatles even made it on stage.
Roy Orbison was a very impressive vocalist.
I have read that Elvis thought Roy Orbison was the best singer he ever heard.