He is certainly not overrated, since I'm pretty sure that would be physically impossible. That being said, he was just acknowledged in the A.V. Club feature "Reinventing the Pencil: 21 Artists Who Changed Mainstream Comics (for Better or Worse)." Don't worry, he was clearly one of the former. So I'm not sure he's underrated either. In fact, I don't know anyone who's familiar with his work who wouldn't rate him as one of the greatest artists ever to work in comics.