The success of a musical depends on the strength of its musical numbers. By this measure “Rock of Ages” is almost a knockout, packing in exhilarating covers of ’80s rock staples. Dramatic deficiencies are drowned out by the intoxicating high coming off the film’s booming pop metal soundtrack.

Like the indulgent and overstuffed nature of hair metal music, the movie contains an excess of plot. “Rock of Ages” has three central conflicts: The first is that of strained relationship between lovers Sherrie Christian (Julianne Hough) and Drew Boley (Diego Boneta), their passion and pain fueling their aspiring music careers. Drew is a barback (not even bartender) for the nightclub known as The Bourbon Room, run by Dennis Dupree (Alec Baldwin) and Lonny Bartett (Russell Brand).

Dupree and Bartett are struggling to keep the venue above water. Hoping for a revival, they look to brooding rock star Stacee Jaxx (Tom Cruise). Unfortunately, Jaxx has begun to doubt his own ability as a musician after having his credibility challenged by Rolling Stone reporter Constance Sack (Malin Akerman). From his and every other character’s inner torment emerges a rollicking set list that propels the movie.

The musical set pieces work mostly because of the performances and original song content, yet the direction renders the choreography almost incomprehensible because much of the dancing takes place outside the camera’s frame. These sequences are further fragmented by editing that doesn’t hold any shot for more than a few seconds, but the acting is still joyously garish.

With mostly poor characterizations, the writing takes a backseat to the acting. There is little chemistry between Sherrie and Drew, who make an unconvincing couple, except in the musical scenes, which can stand on their own. Of all the characterizations, Jaxx’s is the most convincing. What defines him is his ability to enrapture people as a performer. He’s a selfish jerk, but he possesses a rock star charisma that allows him to manipulate people. As a parody of a hair metal band frontman he’s so effective that the character would work in a film that played the material straight.

Outside the performances, the production is outstanding in its ability to evoke late-’80s glam metal. Cinematography, production design, costuming and makeup are all aces. The production effectively establishes and exaggerates the setting to reflect the ideals of the overly theatrical music the movie is based on.

The movie’s cheesy and straightforward elements exist side-by-side without contradiction. “Rock of Ages” is not without genuine flaws, but even the flaws line up with the movie’s excess for the sake of excess attitude.