INDIO, California - The appeal of heavy metal has always lain in its traditions, which are all self-reflexively hokey enough to almost be clichés: the black shirts, the songs about death, the wheeldillee-deedillee guitar solos

Call the first-ever U.S. edition of The Big 4 (the Metallica-headlined day-long metal fest previously held only overseas) a return to tradition, then, as generations of fans descended on the desert to pay homage to the masters of metal, mostly with a beer in one hand and devil horns thrown with the other.

That's not meant to be condescending but rather admiring: this was a cult event on the grandest scale, as over 60,000 estimated attendees with an extremely noticeable all-for-one mindset gathered for similarly structured music all on one stage. (Compare that to the previous weekend's Coachella festival in the same location, with roughly 15,000 more people, all running in majorly disparate directions.)

Even within the genre, the lineup didn't diversify: openers Anthrax, Slayer and Megadeth are all admirable, decades-long carriers of the shreddy, loud/fast/aggressive metal flag -- no cheesy pop, silly nu-metal or any rap-rock hybrid stuff allowed.

Given the focused lineup, it's no surprise the bands delivered, each more crowd-pleasing than the next. Ageless Anthrax guitarist Scott Ian wailed his way through "Among the Living," with bemulleted singer Joey Belladonna bringing a half mic-stand into the audience to allow the crowd to scream along. Megadeth's frontman Dave Mustaine is still snarky and speedy; "Wake Up Dead" was blistering and precise. Of the openers, Slayer were the headbangiest of them all, face-blasting their way through "Dead Skin Mask" and "Raining Blood" before closing with the anthemic "Angel of Death."

But the night unquestionably belonged to the headliners, who delivered a career-spanning, possibly career-defining set that clarified why they've been able to maintain their relevance for so long: simply, it's diversity, stupid.

Emerging onto their two-story stage to an Ennio Morricone spaghetti-western theme, the band plunged into the early '80s with "Creeping Death," guitarist/singer James Hetfield employing the crowd into rally-cry "hey-hey-heys." But unlike some of the openers, it wasn't all how-fast-can-we-play-this-riff; guitarist Kirk Hammett still plays with ambition and delicacy even when he's searching for upper-register peaks, giving his playing a fluidity lacking in many of his contemporaries. It doesn't hurt that the songs are legitimate classics at this point, and the band barrelled through nearly all of its best-known rockers, from the more recent "Fuel" (accompanied, of course, by plumes of fire and ear-shattering fireworks) back to 1988's "One," before closing out the set proper with "Enter Sandman," by far the biggest singalong of the day.

The encore began with an all-bands-on-deck encore cover of Diamond Head's obscure-to-non-metalheads stomper "Am I Evil," historic because it saw notorious rivals Hetfield and Mustaine both hugging and sharing a stage together.

But even that shouldn't be considered all that surprising: as metalheads surely realize by now, when someone understands your traditions, you've got to embrace them, rather than push them away.