Slipknot: Even more than Disturbed, Korn and Chicago's Chevelle, masked horror-movie rejects Slipknot is perhaps the most enduringly intense of the '90s/'00s nu-metal on the Open Air bill — the band's latest album, 2014's ".5: The Gray Chapter," has a new rhythm section and songs as cartoonishly thrashing as they were in 1999. "The thing I learned very quickly in this band is it doesn't have to be a melody to be a hook," frontman Corey Taylor told the Tribune in 2012. "It can be something like the chorus in 'The Heretic Anthem' — 'if you're 555, I'm 666.' So many kids grabbed onto that, it's ridiculous."