I was never a fan of the hip-hop/metal genre, but RATM always played with punk passion, and lyrics that weren't afraid to be brutally poetic. They got the kids involved, making "alternative" music that proposed real alternatives, to get beyond the prescribed program. They put politics back into popular music, and carve out space for like minded artists like Ozomatli and System of A Down.
Sure, they made a lot of money, and that kills your credibility with the critics and cynics, but their fans knew better. Zack gave back to the movement. He was one of the angels that helped make the LA IMC pay its bills. They were the real deal.