For a lover of musical theater, "Sing" ought be a toe-tapping home run. Sampling upwards of 85 song cuts, the film is never without a melody in its step. Something feels oddly missing, though. It's not as fun as it should be. Its characters aren't as engaging or well-rounded as one wishes. And its undernourished screenplay, from writer-director Garth Jennings (2008's "Son of Rambow"), isn't nearly imaginative, warm or clever enough to stand next to the likes of Disney and Pixar's finest. As was the case with their recent "The Secret Life of Pets," Universal's animation arm Illumination Entertainment has not quite mastered the harmony between their ambitious concepts and their scattershot delivery. For every individually wonderful moment, there seems to be a missed opportunity waiting in the wings.

Ever since he was six years old, koala bear Buster Moon (voiced by Matthew McConaughey) has been enamored by the stage—a passion which has led to his ownership of the vaudevillian Moon Theater. Behind on his payments and with the venue threatening to be shuttered, Buster formulates a plan to bring interest back to the theater: hold a singing competition with a $1,000 grand prize. Unfortunately, a flyer misprint on behalf of Buster's dotty old secretary, chameleon Miss Crawly (Garth Jennings), mistakenly touts a $100,000 bounty. Before he figures out this error, he's already held auditions and chosen his competitors—among them, harried domestic pig Rosita (Reese Witherspoon), an overextended mother of 25 children; street-performing mouse Mike (Seth MacFarlane), a crooner with an inflated ego; teenage porcupine Ash (Scarlett Johansson), a hard-rocker with a hidden talent for songwriting; soulful gorilla Johnny (Taron Egerton), yearning to make his musical dreams a reality while dealing with his family's criminal activities; and meek elephant Meena (Tori Kelly), whose stage fright stands in the way of her showing off her big voice. If Buster hopes to make things right and save his business, he is going to need a miracle.

"Sing" is jam-packed with recognizable music vintage and new, most of its voluminous soundtrack cues lasting but a few moments before hurrying on to the next. Director Garth Jennings and co-director Christophe Lourdelet appear to be so focused on referencing as many songs as they can over the course of 108 minutes their script—and the story's pulse—has fallen to the wayside. Simply put, it strikes as a rough draft in need of a polish and further development. With the exception of Meena, warmly voiced by Tori Kelly, the promising characters are not given the time to come into their own or complete their personal arcs.

Matthew McConaughey (2016's "The Sea of Trees") gamely plays Buster Moon, but is this lead protag particularly winning, the kind of plucky underdog a viewer wants to get behind? His earlier scenes where he holds auditions and brusquely pushes most of the hopefuls aside without sympathy or respect permanently taints one's opinion of him. Reese Witherspoon's (2015's "Hot Pursuit") overworked mother Rosita is one of the more likable participants, but her quandary in following her dreams while caring for her children—with little help from her husband, it should be added—is never satisfactorily explored. A would-be charming scene where she cannot help but break into a dance while doing some late-night grocery shopping is undermined by the tired use of Gipsy King's "Bamboleo."

"Absolutely Fabulous" actor Jennifer Saunders (2015's "Minions") can deliciously land any zinger placed in front of her, so her casting as Miss Nana Noodleman, a stately grand dame of the theater asked to judge the competition, would seem to be a perfect match. Unfortunately, it's another missed opportunity, the film tossing her aside too abruptly without taking advantage of this elder diva. Perhaps best of all is director Garth Jennings himself, who voices the picture's most amusing character, Buster's dippy, artificial-eyed Miss Crawly. Miss Crawly is an undeniable descendant of Dody Goodman's scatterbrained principal's assistant Blanche in 1978's "Grease," and Jennings gives himself most of the funniest lines and situations.

"Sing" climaxes, naturally, with the contestants' final musical performances, taking place in a fashion Buster never could have imagined. Each one is fun to watch and listen to—how could they not, with such catchy numbers as Taylor Swift's "Shake It Off," Elton John's "I'm Still Standing," and Leonard Cohen's "Hallelujah?"—but the energy level and overall emotion of these characters' individual achievements seem oddly tempered. As with the film as a whole, the finale doesn't reach the dizzying, melodic heights for which it strives. There is no doubt "Sing" is gorgeously computer-animated, and its heart is in the right place. There is the nagging suspicion, however, that the finished product is only a faint, underwhelming visage of what it could have been. The singing may be in key, but the screenplay is out of tune.