Andy Karl in Rocky
(©Matthew Murphy)

You’ll leave the new Broadway musical Rocky humming the score. Unfortunately, it won’t be the wholly unmemorable one by veteran composers Stephen Flaherty and Lynn Ahrens (Ragtime, Once on This Island) but rather such music featured in the original 1976 film and its sequels as Bill Conti’s stirring theme and the rock hit “Eye of the Tiger” by Survivor, both of which are generously spotlighted.

Oh, did I mention you’ll also be humming the scenery? Christopher Barreco’s elaborate, endlessly shifting sets for this hugely expensive production are indeed awe-inspiring.

The latest in a seemingly never ending series of musicalizations of beloved films, Rocky seemed like a dubious bet for such treatment. Although its storyline about a struggling small-time boxer who finds self-redemption via a one-in-a-million title bout with a reigning champ--as well as love with the mousy girl he inspires to come out her shell--has a powerful elemental quality, its gritty aspects don’t exactly inspire visions of song and dance.

This musical version of the film that made Sylvester Stallone a superstar doesn’t exactly dispel that notion. But thanks to its iconic characters and a brilliant staging courtesy of director Alex Timbers, it emerges as a genuine crowd-pleaser that, much like its titular hero, manages to go the distance.

Co-written by the incongruous team of Stallone and Thomas Meehan (Annie, The Producers), the musical is slavishly faithful to its inspiration, telling the Philadelphia-set story of Rocky Balboa (Andy Karl), the “Italian Stallion” who’s reduced to low-end bouts and making a living as an enforcer for a loan shark. He’s desperately in love with Adrian (Margo Siebert), the sister of his best friend Paulie (Danny Mastragiorgio), but although she returns his affections she’s far too repressed to act on them.

Rocky’s life changes when he’s suddenly plucked out of obscurity to fight the champion, Apollo Creed (Terrence Archie), after his original title bout opponent is injured. Creed, who picked Rocky because of his colorful nickname and appealing hard luck story, expects to make short work of the untested fighter. But as everyone in the audience undoubtedly already knows, that’s not to be the case.

The sluggish first act recreates many of the film’s iconic scenes with a slavish fidelity that inspires boredom. Rest assured that you’ll hear Rocky bellow “Yo Adrian” more than a few times and that you’ll be reintroduced to such familiar characters as his snappish trainer Mickey (Dakin Matthews). Flaherty and Ahrens’ ballad-heavy score is similarly uninspired, with the exception of one or two catchy songs like Rocky’s solo number “My Nose Ain’t Broken.”

But director Timbers really kicks things up a notch in the second half with a couple of exuberant training montages and particularly with the climactic boxing match featuring terrific pugilistic-inspired choreography by Steven Hoggett and Kelly Devine. To reveal the details of the incredibly inventive staging would be to spoil the surprise. Suffice it to say that it involves a movable regulation-size boxing ring, a giant multi-screen Jumbotron, and an all-around immersive quality that truly involves the audience in the action. To say that all the hoopla was greeted by rapturous cheers would be an understatement.

Karl, although a bit too slight to make for a convincing heavyweight, brings real charm to the role, channeling just enough of Stallone to satisfy the film’s fans while also making it his own. The supporting players, by contrast, pale in comparison to their cinematic predecessors. Seibert’s Adrian lacks Talia Shire’s sublime poignancy, and Mathews, Archie and Mastrogiorgio fail to supply the comic grace notes that Burgess Meredith, Carl Weathers and Burt Young infused into their performances.

On the way out, a fellow critic commented, “What are we even doing here?” It was an apt question. For all its flaws as a musical, the show feels genuinely critic-proof. It seems very likely that Rocky will be fighting at the Winter Garden for a long time to come.

Winter Garden, 1634 Broadway. 212-239-6200. www.telecharge.com.