Chasing brunch to the brink of apocalypse is Stephen Sondheim at his most extreme, and the world premiere of “Here We Are,” which opened Off Broadway at the Shed on Sunday, is a study in overabundance. 

Appetite for the late composer’s final musical, written with David Ives and directed by Joe Mantello, has made it a hot ticket among those familiar enough with the moneyed types depicted onstage to potentially be the butt of the joke. Though Sondheim made light sport of critiquing bourgeois mores in shows like “Company” and “Merrily We Roll Along,” here the rich are served hot like a bottomless buffet.

And let’s cut straight to the sweet stuff: Performances from the pinch-me-this-can’t-be-real cast are like a Broadway gourmand’s fever dream. Whatever else this deeply strange and Frankenstein-ed musical delivers — which is a lot — the production’s outrageous lineup of stars are as delectably odd as they’ve ever been (yes, even Denis O’Hare). By the time David Hyde Pierce makes a late act-one entrance as a martini-swilling bishop who covets designer heels, the needle on one’s pleasure odometer simply snaps off. That “Here We Are” ultimately doesn’t know when to stop becomes easy to forgive.    

Developed over the decade prior to Sondheim’s death in 2021, the musical draws inspiration from two films by avant garde director Luis Buñuel, whose surrealism and social satire bind the show’s two stylistically disparate parts together. 

The first act, modeled after “The Discreet Charm of the Bourgeoisie” (1972), follows a gaggle of frivolous friends (plus a token revolutionary, played with droll militancy by Micaela Diamond) on their frustrated quest for midday repast. Urbane and bizarre, it has the uncanny feel of an amusement park ride, with servers (played by O’Hare and scene-stealer Tracie Bennett as a series of severe European matrons) who frustrate rather than soothe their needy patrons. The herd ultimately retreats to the estate of Steven Pasquale’s louche lothario, where they finally dine.

Only it might be their last supper. Act two, drawn from “The Exterminating Angel” (1962), finds them trapped in an ornate study while doomsday looms outside. Book-lined and elaborately furnished, the room hems in its captives with slick-black walls and gold trim, a stark contrast to the first act’s laboratory-white, blank abyss. David Zinn’s set and Natasha Katz’s lighting are marvelous signifiers of mood and money, and serve as a primed canvas for Zinn’s splendid costumes, which do nearly as much identifying work as the stars who wear them.

Wafting about in a flowy, sky-blue negligee, Rachel Bay Jones’ lady of leisure is daft but sweet and accidentally profound. Her husband, a plush tracksuit-clad Bobby Cannavale, less distinctly drawn, could be any number of swaggering loudmouths the actor has played before. And their married pals, played by Amber Gray and Jeremy Shamos, are as image-obsessed as their posh-professional off-duty looks suggest — until, of course, they aren’t. Who could be when the only available toilet is a Ming vase in a closet?    

The “we” in “Here We Are” — including a colonel played by an underused Francois Battiste and a soldier-turned-lover played by Jin Ha — are broadly sketched types. These are not psychologically complex characters whose interior lives are clarified in song, as many of Sondheim’s other scores have done. Aside from a hallucinatory second-act reverie that gives Jones a production high point, waiting for the end times proves less tuneful. A grand piano onstage inexplicably stops working, a nod to the coming end of the world. (“The Exterminating Angel” does not have a score.)

That unevenness is by design, the creators say, not because Sondheim’s work was left unfinished. His score to the first act, an itinerant black comedy, features motifs familiar from shows like “Into the Woods” (bouncy, wordy, existential), and the composer trying out a looser hand with profanity. There is at least one dud (about a restaurant that’s out of everything), but hearing new Sondheim, at times harshly amplified here, is a thrill on its own. 

But the combination of Sondheim’s score with Ives’ absurd and often hilarious book, rather than generating synergy, feels uneasy and disjointed, like they’re pulling in opposite directions. Partly that’s because the plot itself only stumbles forward, first through non sequiturs and then inevitability. Two thin subplots are extraneous, including one that saddles Battiste’s homeland security officer, the only dark-skinned person onstage, with trauma that evokes little more than a loose end. Once the social satire of “Here We Are” has been established, the question merely goes from whether the rich will eat brunch to whether they’ll eat each other. 

Appropriately enough, prodding the elite without actually eating them has become a perennial plat du jour at the Shed, where other recent shows, like “Straight Line Crazy” and “Help,” have gestured at condemning the privilege and inequality that resulted in the Hudson Yards megadevelopment without much bite. 

“Here We Are” delights in the flavor of its vapid jet-sets, but ultimately spits them out in a resolution that betrays its own internal logic. It’s too much, and robs the show of its potential teeth. Better to know when the feast is done.