IMHO Rick Rubin is a great producer; Johnny Cash:"The Man Comes Around", Tom Petty, Beastie Boys, U2, RHCP the list goes on. He was credited for the merging of rap with heavy metal if that's not huge to some. Personally I was not a fan of St. Anger and Rick Rubin guided Metallica back from the dead with this new album. They made a huge turn from St. Anger and only can get better from here out.