Here is a sampling of what they had to say:
Rob Kendt in his Broadway.com Review: "As sharp and glistening as a straight-edge razor, director John Doyle's stripped-down concert/theater rendition of Sweeney Todd gives the kind of buzz you don't expect, and certainly almost never get, from a Broadway show. It is the distinct hum of musical and theatrical intelligence; it is the glow of sheer brilliance as an entertainment value in itself... By having the 10-member cast play the score while they act and sing the show, Doyle's production makes the show's craftsmanship lovingly, nakedly transparent the deft new orchestrations are by Sarah Travis. What this production lacks in definitive acting turns, vocal virtuosity, and realistic staging—and it does have some deficits in all these departments—it gains in intimacy and intention... LuPone relaxes into this witchily sympathetic role with supreme confidence. She doesn't push or prod a single moment, nor does she oversell either Mrs. Lovett's craven, amoral practicality or her sweeter, dafter romantic side. Whether she's cleaning the tools of her dismembering trade or draining spit from her tuba, LuPone gives us a wonderfully undespairing anti-heroine."
Ben Brantley of The New York Times: "The thrilling new revival of Stephen Sondheim and Hugh Wheeler's Sweeney Todd: The Demon Barber of Fleet Street, which opened last night at the Eugene O'Neill Theater in a production starring Michael Cerveris and Patti LuPone, burrows into your thoughts with the poisoned seductiveness of a campfire storyteller who knows what really scares you... Though it uses only 10 musicians instead of the original 27-piece orchestra, this Sweeney never stints on the music's drama, intricacy or sheer beauty. Your ears don't just coast on a symphonic sweep. Every note and sound, whether from a plucked violin string or a tinkling triangle, seems to count fully... Mr. Cerveris's stunningly realized Sweeney seems destined to haunt the nightmares of anyone who sees him."
Clive Barnes of The New York Post: "The cast is tremendous, keeping the proceedings going with such style, simplicity and involvement that they make it impossible to imagine the musical being performed in any other way or by anyone else. As Sweeney, a surly, vibrant-voiced Cerveris dominates the action, getting crazier as the body count mounts. His viciousness is matched by a wonderful LuPone—and, yes, she plays the tuba! Her intonations and timings are impeccable, with just the right combination of chirpy English Music Hall and flamboyant Grand Guignol melodrama. This is an extraordinary evening: unexpected, thrilling and, in the oddest way, authentic."
David Rooney of Variety: "Plunging the show back deeper into the Grand Guignol roots whence Sondheim and book writer Hugh Wheeler plucked it, and adding a liberal splash of Brecht-Weill haut-performance alienation, Doyle's mercurial reinvention enlists 10 cast members on a single set to do double duty as actors and orchestra, most of them playing multiple instruments. The result becomes mesmerizing on a number of levels. The gruesome tale of the demon barber and his amoral accomplice Mrs. Lovett remains a compelling yarn, building here to a chilling climax in which horror is given a disquietingly human face. It fascinates no less as an exercise in theatrical artifice, reminding of the evocative power of stagecraft to elicit thought, stimulate imagination and summon atmosphere. It peels away layers to reveal the dazzling intricacies of Sondheim's choral and orchestral structures under something akin to a musical microscope. And as a display of focus and technique, there can be few experiences equal to watching the prodigiously talented cast grapple with such a demanding score and complex lyrics while remaining in character, not to mention wielding props and often cumbersome instruments in moves choreographed with unerring precision."
Michael Kuchwara of The Associated Press: "This is a singular Sweeney, a delightfully idiosyncratic interpretation that, thankfully, is more a rethinking than a reproduction. Directed and designed by John Doyle, this compact adaptation of the show is done with only 10 actors the original had more than two dozen who also double as the show's musicians. It challenges memories of that 1979 production by inviting theatergoers to re-examine the show's book and score on entirely different terms. Doyle's take on the show strips Wheeler's story to a directness that underlines the terror of the tale, set in 19th century London. It's genuinely creepy. Musically, Sondheim's songs are delivered in such artful simplicity that they sound remarkably fresh and clear, thanks to Sarah Travis' new, lean orchestrations. And another level of enjoyment exists, too, watching the actors negotiate various instruments—with surprising success."
Elysa Gardner of USA Today: "This Sweeney Todd, which opened Thursday at the Eugene O'Neill Theatre, is as thrilling as it is bold. Travis' spare, spooky arrangements may not have the majestic sweep of Tunick's, but they're perfectly suited to Doyle's staging... Luckily, Doyle, who introduced this production in the U.K. with different performers, has acquired a company whose virtuosity is matched by a breathtaking chemistry. This is especially true of Michael Cerveris and Patti LuPone, who play the avenging Todd and Mrs. Lovett, the piemaker who devises a scheme to make his bloodlust profitable. I had seen LuPone tackle Todd's adoring, amoral accomplice in a concert staged with the New York Philharmonic and was less than riveted. But under Doyle's guidance, her Mrs. Lovett becomes less cartoonish, at once funnier and more chilling in her wily desperation. Cerveris is equally impressive in a more demanding part."
Linda Winer of Newsday: "Is John Doyle's stripped-down, modern-dress production the only Sweeney Todd we need to see again in our lifetimes? Certainly not. Is it intensely musical, constantly surprising and bloody buckets of fun? Absolutely. We lose things, but then we find things in this high-concept reimagining... The score is a supremely well-executed piano reduction, with dark strings and winds for exquisite splotches of emotional spot color. The exposed instrumental colorations can be rough as often as they are pithy and transparent. Beautiful sound is sometimes sacrificed for concept. But—perhaps more important—we also hear every nuance of every brilliant and hysterical Sondheim word and masterly rhyme... Manoel Feliciano, gifted singer and violinist, is essential as an antidote to any sense of asylum contrivance. Benjamin Magnuson has an insistent clarion ardor as Anthony, the sailor who loves Sweeney's abducted daughter Johanna - played with a welcome spunkiness along with the high-operetta lyricism by Lauren Molina. Both are endearing on cellos.
Mark Jacoby is aptly disgusting and tormented as the libidinous Judge Turpin, whose lighter-than-customary voice overlaps with Sweeney's for a 'Pretty Women' of contrary motion and ironic sweetness. Alexander Gemignani, apparently running everything from the piano, is chillingly imperious as the Beadle. Pirelli, the Italian comic barber, is played by Donna Lynne Champlin in male drag, invaluable throughout on the accordion."