It's very simple. If you like rock songs and power ballads hailing from the 1980s—and let's face it, who doesn't?—then "Rock of Ages" will be tough to resist in spite of its ungainliness. A big-screen adaptation of the 2009 Tony-nominated Broadway musical, the film is stuffed virtually wall-to-wall with catchy, recognizable tunes performed by an ensemble cast mostly going through the motions of a shaggy old "making-it-in-L.A." romancer. As directed by Adam Shankman (2007's "Hairspray") and written by Justin Theroux (2010's "Iron Man 2"), Chris D'Arienzo (2010's "Barry Munday"), and Allan Loeb (2011's "Just Go with It"), the narrative wanders around trying to keep track of all its characters (including some who have very little point in being there at all) while ultimately inflating itself just past the two-hour mark. Yeah, it's kind of repetitive and something of a mess, but every time the chords of another classic song strike up, game audiences will find the movie's eager-to-please, "Don't-Stop-Believin'" charms to be next to irrepressible.

Urged by her wise grandma to escape her dusty hometown in Oklahoma and make something of herself, fresh-faced Sherrie Christian (Julianne Hough) heads for Hollywood with dreams of becoming a singer. In the meantime, she needs to make money, and after she is promptly mugged, kind barback and wannabe-musician-with-a-case-of-stage-fright Drew Boley (Diego Boneta) comes to her rescue by helping to get her a waitressing job at The Bourbon Room. Owned by Dennis Dupree (Alec Baldwin), he and faithful assistant Lonny (Russell Brand) are hoping that their upcoming concert of Arsenal, promoted as sexy, egotistical rock god Stacee Jaxx's (Tom Cruise) band farewell before going solo, will be enough to save their financially ailing business. As Sherrie and Drew start to fall in love, they are warned that fame changes people and relationships. In a city built on rock 'n' roll, however, it is Patricia Whitmore (Catherine Zeta-Jones), tight-pantied wife of philandering right-wing mayor Mike Whitmore (Bryan Cranston), who will stop at nothing until she cleans the streets of Satan's music and closes down The Bourbon Room for good.

"Rock of Ages" stacks single songs and the frequent mash-ups atop each other with such fervent relish that it creates the feel of a highway pile-up. Trading in a smooth storytelling rhythm for a greatest hits compilation in cinematic form, the picture is overstuffed, even clumsy, before all defenses are torn down in time for another reminder of why the '80s were such an iconic era for music. Def Leppard, Poison, REO Speedwagon, Bon Jovi, Scorpions, Starship, Foreigner, Quarterflash, Warrant, Journey, Night Ranger, Pat Benetar, Twisted Sister—the sheer breadth of artists whose songs get covered, each one cleverly placed to comment upon the story and characters at any given moment, more than makes up for director Adam Shankman's spotty direction and Emma E. Hickox's (2007's "Blood and Chocolate") occasionally unfocused editing. Indeed, while most of the numbers are choreographed well, there are a few (like "Shadows of the Night," losing sight of singer Mary J. Blige's empathetic gentlemen's club owner Justice Charlier in a sea of writhing, pole-dancing bodies) that are cut too quickly and have trouble figuring out what the camera should be trained upon. Furthermore, other song performances that should be more intimately about two people awkwardly segue to other characters in different locations also singing along. 1999's "Magnolia," this is not, and aside from giving extra screen time to the supporting actors, their incorporation doesn't always feel organic to certain set-pieces and takes the viewer out of the moment.

In a film that sticks close to the surface, one thing that can be counted on is how fun it is to see all these '80s rock chestnuts combined into one big coherent smorgasbord of sounds. Highlights include Foreigner's "Waiting for a Girl Like You," which captures the anxious, dreamy electricity of Sherrie's and Drew's first date, leading to a nighttime scene set at the Hollywood sign; the same band's "I Want to Know What Love Is," a part-steamy, part-boisterously absurd duet as Stacee Jaxx seduces bespectacled Rolling Stone reporter Constance Sack (Malin Akerman), her dignity falling away with each stitch of clothing; Quarterflash's "Harden My Heart," following the heartbroken and suddenly jobless Sherrie as she's taken in by Justice, owner of the Venus Club; and Poison's "Every Rose Has Its Thorn," wherein a parted Sherrie and Drew both face a harsh reality they're not proud of. One of the most talked-about and crowd-pleasing sequences is sure to be Dennis' and Lonny's take on REO Speedwagon's "Can't Fight This Feeling" as the two men's hidden love for each other rises to the forefront. It straddles the line between silly and sweet, which is about right for any love song between a sly but appreciably reeled-back Russell Brand (2011's "Arthur") and the always-welcome Alec Baldwin (2009's "It's Complicated").

The plot is flimsy, and so are its conflicts—the whole story thread with picketing mayor's wife Patricia Whitmore is practically a non-starter until the third-act payoff, and there's never any comeuppance involving her cheating husband—but the actors look to be having a grand time. Of the two leads, the vivacious Julianne Hough (2011's "Footloose"), as Sherrie, is the stronger actor while newcomer Diego Boneta, as Drew, one-ups her in the vocals department. Hough can carry a tune, no doubt about that, but her baby-doll singing voice lacks the gravel to do these kinds of songs proud; she's more effective as a likable, vulnerable presence. In comparison, Boneta is a veritable shape-shifter as his character goes through very physical changes, from sweaty, leather-clad rock singer to squeaky-clean boy band member. He's a versatile singer, but is better at putting on faces than outwardly expressing his emotions.

The rest of the ensemble are fine warbling their way through their songs—there are no offenders here like Pierce Brosnan in 2008's "Mamma Mia!"—with Tom Cruise (2011's "Mission: Impossible – Ghost Protocol") particularly impressing as he transforms his usual clean-cut, upstanding image into booze-swilling, half-naked rocker Stacee Jaxx, a guy so famous that he's lost sight of who he was before women started throwing themselves at him. Constance sees right through this, and it's her harsh but true reading of his loneliness and superficiality that leads him to view her as more than just an easy conquest with tits. As Constance, Malin Akerman (2012's "Wanderlust") is a beautiful singer and arguably the picture's secret comedic weapon as she not only holds her own against Cruise, but threatens to overshadow him—quite a feat here. Catherine Zeta-Jones is a game participant as narrow-minded villainess Patricia Whitmore, especially when she and her church board members perform Pat Benetar's elaborately choreographed "Hit Me with Your Best Shot," but she too often gets lost in the shuffle. As her slimeball husband, Bryan Cranston (2011's "Drive") fares even worse, no fault of the actor's. Last but not least, Mary J. Blige proves that she needs her own film, tearing it up in every way possible as Sherrie's boss and confidante Justice. Blige brings such soul to her every second—even in moments when viewers may be asking themselves what she's doing there, singing a song that a more pertinent character is simultaneously belting out across town—that she more than makes up for her underwritten role.

A bit tiring and respectively on the long side at 123 minutes, no one, at least, will be able to say they didn't get their money's worth when they step foot in a theater showing "Rock of Ages." The mid-section could have used a trim—though entertaining, the material with Stacee Jaxx gets in the way of focal points Sherrie and Drew, and a little of his pet monkey (named Hey Man) goes a long way—but what never flags is the natural energy of the fab '80s beats and the sincerity of Julianne Hough's and Diego Boneta's spry turns. The music, like the "movie" written about in the lyrics of Journey's most famous song, "goes on and on and on and on," and that is a very good thing. Imperfect though it is, "Rock of Ages" has the power to have a person pining in no time for the days of big hair and bigger pipes, a decade that somehow, in retrospect, feels a lot more innocent, whether it actually was or not.