Rock of Ages, a new star-clogged pop-musical diversion, is a cinematic event. It's not every day, after all, that you get to see two great American traditions — guitar/bass/drums rock music and Tin Pan Alley musical theater — so thoroughly, mutually degraded.

This mess originated as a stage production, first performed in Los Angeles in 2006, from which it spread to Broadway, the West End and the known universe beyond. Like Mamma Mia! or Jersey Boys, it belongs to the species that has been dubbed the “jukebox musical,” in which a group of licensed pop songs are strung together to create a ready-made musical score. This practice of steering a story between pre-existent tunes effectively guarantees that the songs cannot grow from the plot organically, while challenging the author of the book to invent the pretext of a narrative setting in which to imbed the numbers.

In the case of Rock of Ages, the foundations that a story must be built upon are an afternoon of VH1 Classics' worth of 1980s hair metal. Original author of the stage show, Chris D'Arienzo, is joined for the screenplay by Justin Theroux and Allan Loeb, and they have together drafted something that combines elements of Menahem Golan's The Apple, Empire Records, the Guns N' Roses video for “Welcome to the Jungle” and Tipper Gore's '80s career as politician's wife and PMRC scold.

It's West Hollywood, 1987, and a bus pulls up to a corner to disgorge … not Axl Rose with the hayseed's straw sticking out of his mouth but Dancing With the Stars mainstay Julianne Hough, here playing Sherrie, a girl from Tulsa dreaming of the big time as a frontwoman. Instead, she gets her suitcase stolen and ends up waiting tables at the Bourbon Room — a Whisky A Go Go stand-in, located on a rebuilt vintage Sunset Strip — thanks to the intervention of young Drew (Diego Boneta), who we know is destined for Sherrie, as he shares her scruffily clean-cut looks and her wide-eyed Juke Box Hero aspirations and is, like her, staggeringly dull.

Even this safe haven is not, however, safe. “Taxes, they're so un-rock & roll,” Bourbon owner Dennis (Alec Baldwin) sighs, faced with a money-crunch deadline as the mayor's Tipper-esque anti-rock crusader wife, Patricia Whitmore (Catherine Zeta-Jones), scrutinizes the Bourbon's fudged books, looking for any excuse to shut the place down as part of her “Clean Up the Strip” initiative. Dennis' Hail Mary solution is corraling back Stacee Jaxx (Tom Cruise), former Bourbon mainstay turned decadent, dissipated and totally unreliable arena rocker, for a one-off benefit show.

Cruise has the advantage of playing one of those built-up parts, like Harry Lime, or Hickey in The Iceman Cometh. Everyone in the first act talks up Stacee Jaxx, so he can't help but be impressive by the time he shows up — a fine fit for a star who by now can really be only convincing as a star. The dissolute rock-god gags (pet monkey, scrums of groupies) are old-hat, but Cruise is a dynamic, kabuki-esque, full-body performer, and he gives Jaxx something between the boozy silverback swagger of Jim Morrison and Glenn Danzig's armored-car physical presence.

Jaxx finds his match in Malin Akerman's Rolling Stone reporter, who calls out Jaxx's coasting career under Paul Gill (Paul Giamatti), his manager — that most conveniently villainized of rock-historical figures, scapegoated so that personal accountability can never be demanded of our heroes. Gill says things like, “We did a whole focus group on this — numbers don't lie” (which probably tested well) and will later get his hooks into rising star Drew, drafting him in a New Jack Swing-style boy band. This is presented as the epitome of sellout, which only makes sense if you are willing to accept the premise that there was more artistic integrity in being a member of, say, Poison, than in being in New Kids on the Block. Like much in Rock of Ages, it also carries a faint whiff of unexamined racism.

Choreographer-cum-director Adam Shankman, who previously handled 2007's Hairspray, does his best to keep things assaultively lively, hot-potatoing songs around the cast and crosscutting in Frankensteined mash-ups. The songs in Rock of Ages split pretty evenly between power balladry (“More Than Words,” “Every Rose Has Its Thorn”) and anthemic fist-pumpers (“Pour Some Sugar on Me,” “Here I Go Again”).

There are two basic ways of thinking about this music; which one you're inclined toward probably will influence your enjoyment. One is fond nostalgia — this was innocently hedonistic good-time party music, with hooks big enough to land Moby-Dick. “Goddamn, they don't make 'em like they used to,” said Mickey Rourke's Randy “The Ram” in The Wrestler, when Def Leppard comes on in a bar. “Then that Cobain pussy had to come around and ruin it all.”

The other — which I happen to believe — is that that Cobain pussy did everyone a great favor, because hair metal was bone stupid, creatively bankrupt, morally debased pop trash that marked an all-time low in record-label-chart manipulation and synthetic hit-making hackery. And if rock, as is herein insisted, will never die, the “rock” paradigm perpetuated by Rock of Ages–the same as in Rockstar energy drink and Nickelback's “Rockstar”– deserves a deep, dank, unmarked grave.

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