Even though Master of Puppets didn't take as gigantic a leap forward as Ride the Lightning, it was the band's greatest achievement, hailed as a masterpiece by critics far outside heavy metal's core audience. It was also a substantial hit, reaching the Top 30 and selling three million copies despite absolutely nonexistent airplay. Instead of a radical reinvention, Master of Puppets is a refinement of past innovations. In fact, it's possible to compare Ride the Lightning and Master of Puppets song for song and note striking similarities between corresponding track positions on each record (although Lightning's closing instrumental has been bumped up to next-to-last in Master's running order). That hint of conservatism is really the only conceivable flaw here.