American Head Charge and No One opened this night’s edition of the confusingly-titled “Pledge Of Allegiance Tour” with a pair of short, modestly engaging modern metal workouts, marred a bit by dodgy sound and by the fact that both bands were jammed up against the front of the arena’s rather robust stage, evidently banned from touching the cool stuff that the big boys brought. Hard to get your mojo rising under such circumstances — although American Head Charge did manage to stir some mosh pit action with their Sons of Ministry sound, no mean feat for openers playing at 6:15 PM.

Teutonic industrial nihilists Rammstein certainly didn’t lack for mojo power. Singer Till Lindemann opened his set by lighting himself on fire — his coveralls burning not for the usual 10 seconds or so, but through the entire song instead. Wow. And wow to the titanic floor-to-ceiling fire blasts that instantly raised the temperature in the room by at least 10 degrees each time they exploded, and to keyboardist Flake Lorenz’ dental office styled keyboard setup, and to Lorenz and Lindemann going at each other with face-mounted flame throwers, and to Lindemann abusing Lorenz with a hydraulic, high-pressure, trouser mounted, uh, thing. And wow to the music, which rocked, hard, made you stomp and sweat and scream along, even though you had no idea what the German lyrics meant. As it was unfolding, my friend Russell looked at the smoking stage and said “All of a sudden, the fall of the Roman Empire makes perfect sense to me.” Yep.

System of a Down followed, impressively, ripping through all but four of the songs on their latest album, Toxicity, balancing the plate with four choice cuts from their eponymous 1998 disc. The overall effect was hair-raising, as their smart, powerful, oftentimes beautiful songs were ignited by the mass sing-alongs that accompanied them, and illuminated by some of the best behind-the-stage film projections since the Butthole Surfers retired their penile reconstruction surgery films in the early ’90s. Imagine this: several thousand kids intoning “Father, into your hands I commend my spirit . . .” while watching aerial desert shots–much like those that other earnest young people were flying over, deep in harm’s way, even as we sang. Chilling.

As are many of System of a Down’s songs. The Armenian-American, Hollywood-based quartet have crafted a truly groundbreaking body of metal-flavored music, deploying melody lines straight out of their Armenian folk music heritage, composing lyrics about life, love, war and death that stand alone as rich poetry in their own rights, singing harmony parts culled from Orthodox high mass, creating tension-building soft-slow-sweet parts, then detonating them with a ferocity and glee that’s without parallel among their contemporaries. Guitarist Daron Malakian tried to downplay the power of his group’s material at one point, wryly imploring “All of our songs are about drugs and sex . . . don’t take us too seriously.” But he’s wrong, and System of a Down do deserve to be taken seriously, standing today in this critic’s eyes as the world’s most impressive, important metal band.

And Slipknot? Ehhh . . . not so important. Like Rammstein and System of a Down, the Iowa-bred, fully-masked nine-piece offer an over-the-top visual spectacle, and are louder than all of hell’s bells and whistles combined — but they just don’t have the strong songs to make their spectacle really matter. Volume and clarity were the other big problems Saturday night, as the density of the material being flung from the stage made it hard to differentiate one sound from another in the aural onslaught.

The final problem with having nine guys in a metal band is that most of the time there’s not enough for all of ’em to be doing — so after several songs worth of watching two band members, one in a clown mask, one in a bondage mask, kneeling atop their custom drums, shaking their oo0-scary heads, any sense of menace or awesome power was replaced by simple smirk-induction, as the spectacle got to be pretty damn stupid, pretty quickly. Slipknot lost points for their pentragram/goat’s head Satanism backdrop, too. Gonna have to do better than that to scare anyone in these heavy times, guys.