Matt Doyle Photo by Matthew Murphy.

It's not just that this show, by Ryan Scott Oliver (book, music, lyrics, and orchestrations) and Hunter Foster (book) is grossly overamplified (by sound designer Ed Chapman), to the point where lyrics are unintelligible when more than three people are singing at once. It's that everything, from the writing to the direction (Brandon Ivie) to the choreography (Lorin Latarro), has the volume pegged at 13, regardless of whether that's ever the right choice.

Simplicity would seem to be the best way to approach the ostensibly quiet tale of the titular hero (Matt Doyle), who dives off of a cliff to save his best friend Agnes from drowning, and ends up in the underworld. Convinced that he's still alive and that he can return Agnes in one piece, he begins searching for her, during which time his ability to help the dead remember their lives makes him a messianic figure and he befriends a sharp-edged tour guide named Gretchen (Allison Scagliotti) and encourages her to rekindle her own hope.

The shape of the story is solid, and there's power in the relationship that builds between Jasper and Gretchen as he slowly loses his memories of life and she quickly regains hers. And the final song, "One More Day of Snow," describing the complex emotions at play in the aftermath of Jasper's journey, is a genuine winner you'll be humming out of the theater and quite probably well into the next day.

But the best moments, and most of the tangible feelings, get lost amid what too often feels like a cut-rate Glee–meets–American Idol knock-off. The opener ("Hello, Jasper!") is catchy, yes, but hyper-caffeinated, an off-putting blend of boundless energy and plastic emotions, and Latarro's choreography, which depends so much on sharp arms and violent intensity, looks ripped from a drug-drenched music video. Most every scene builds on these elements, apparently unintentionally, with Oliver's basically attractive rock-pop compositions erupting in giant walls of mush, and each of the nine actors lunging and lurching about as though they're auditioning for roles as theme park animatronics.

The most robotic is Doyle, a usually reliable performer (he was terrific as the doomed cousin in War Horse) who here is all bad habits and falsity. Though he displays a genial personality and sings well, his every motion looks intended to fill the rear balconies at Radio City Music Hall (the West End seats fewer than 100); every inhalation before a musical phrase is done as though the fate of the universe were at stake, and his frequent high notes appear calculatedly effortful. Nothing about Doyle's work signals youth, innocence, untapped passion, or unfettered affection, which are among Jasper's most defining traits.

Ben Crawford pours on the glower like maple syrup on pancakes in playing Jasper's nemesis, Lethe, but hardly projects a convincing threat. Scagliotti manages what most of the cast members do not, and intermittently comes across as vaguely human, though the abrasive, sarcastic personality she floats most of the time is rather less endearing than Foster and Oliver want us to believe.

To be fair, almost everything seems chosen for effect rather than appropriateness. Thirty minutes (at most) of action here require two and a half tedious hours, the extra time devoted to exploring the full panoply of afterlife personalities, with major Greek, Roman, Egyptian, Norse, and literary (Dante's Inferno is invoked), many of whom stay just long enough to model Bobby Pearce's flamboyant costumes and perform a song or scene. There's no coherence or point to any of this, and when Hel and Loki (Bonnie Milligan and F. Michael Haynie, trying oh so very hard) start singing about their genitalia, Beatrix Portinari (Milligan) croons a country love song, a redneck hick named Chuck (Haynie) blusters on to run a water-bottling factory at full-bore stereotype, or Pluto (Leo Ash Evens) stamps about like a spoiled brat after being spurned by an indifferent, Bronx-born Persephone (Andi Alhadeff), you're yanked out of the show rather than drawn in.

If Ivie has done nothing to rein in the proceedings, he also never runs short of ideas as far as staging them. Masks and puppetry play crucial roles in conjuring wonders, and the swimming scenes, rendered with de rigueur flapping blue fabric, are beautiful and dramatic; like the unprepossessing set (by Patrick Rizzotti) and lights (Herrick Goldman), they work precisely because they deliver exactly what is required and not a stitch more.

That lesson needs to apply to everything else. Though it's currently being trampled by enough steamroller "theatricality" (scare quotes included) to make Mel Brooks blush, there's a captivating, moving show here someplace. But Oliver and Foster aren't likely to find it until they first divest Jasper in Deadland of its dead weight.

Jasper in Deadland
Through April 13
West End Theatre, 263 West 86th Street between Broadway and West End Avenue in the Church of St. Paul & St. Andrew, second floor
Tickets and performance schedule at www.prospecttheater.org