The singular production of "Sweeney Todd" that opened Thursday night at the Eugene O'Neill Theatre is, in some ways, more significant for what it does than for how well it does it.

British director John Doyle has gone where few men have gone before. Rather than follow the Broadway model of sticking close to the original when staging a revival of a well-known show, with nuances here and there, he's deconstructed "Sweeney Todd" and reimagined it.

The acclaimed original production of the Stephen Sondheim-Hugh Wheeler musical, in 1979, offered a large-scale, sumptuous evocation of 19th-century London in telling the story of a demented, murderous barber. The Broadway revival 10 years later was greatly reduced in scale but followed the same dramatic path.

What Doyle has done is yank the story out of its Victorian era, a setting that would have seemed as essential for "Sweeney Todd" as the Russian village of Anatevka is for "Fiddler on the Roof."

He's set the blood-soaked story, which stars Michael Cerveris as Todd and Patti LuPone as Mrs. Lovett, in what appears to be a modern-day insane asylum, and the gripping opening image is of a character being released by a white-coated doctor from a straitjacket and ungagged, so that he can ask us to "attend the tale of Sweeney Todd."

The depraved and deluded characters in the musical command our attention in a fresh way, not only because the intimate, single-set production has them all onstage throughout the evening, but because they double as the show's orchestra, playing instruments ranging from cello to accordion.

The reduction of the orchestra - the cast has only 10 actor-musicians, not all of them playing their instruments at the same time - means much of the sumptuous beauty and majesty of Sondheim's music is lost.

The compensation is the way the music, through the instruments, becomes closely tied to each character. Todd's virginal daughter, Johanna (Lauren Molina), plays the cello, and the image of her playing and the music she makes become part of who she is, creating a resonance you feel more than understand.

The orchestrator, Sarah Travis, is one of the heroines of the evening, superbly arranging the music for the small orchestra in a manner that carries through melodic themes and underlines the horror-story drama, yet also has considerable wit, as in a brief musical dialogue between a flute and a violin.

As singers, the performers fully honor Sondheim's remarkable lyrics, his sheer, euphoric joy in words, and the many ways he can get them to rhyme and amuse us. ("Being careful with your coriander, that's what makes the gravy grander.")

This is a show whose impact slowly builds. At first, the tale of Todd, who's escaped from his life sentence to exact revenge on the judge (Mark Jacoby) who falsely imprisoned him in order to get his hands on Todd's innocent young wife, is somewhat distant. There's almost the feeling of watching a concert version of the musical.

Cerveris seems young for his role, although the fierceness of his performance makes you forget his age pretty quickly.

There's some questionable added humor.

Wheeler's book and Sondheim's lyrics already provide a fair amount of laughs, to make the horror tolerable. But Doyle introduces more and broader comedy.

Much of it is in the hands of LuPone, whose easygoing style as the opportunistic Mrs. Lovett (who turns Todd's victims into pies and profit) makes her the most accessible character.

Often amusing, LuPone at times overdoes it, as when, clad in a miniskirt, she ostentatiously wiggles her ample backside while puffing on a tuba. (Her playing, which is occasional, is more for comic than musical effect.) Her characterization robs "By the Sea," in which Mrs. Lovett fantasizes about marriage and a normal life with Todd, of much of its poignancy.

Also played for laughs at times are the young lovers, Johanna and Anthony (Benjamin Magnuson). Admittedly, they're not the most compelling characters in the story, but a humorous approach means that when Anthony sings the beautiful, yearning love song "Johanna," it's hard to connect to his emotions.

Aside from Cerveris and LuPone, Alexander Gemignani, as the officious beadle, and Manoel Felciano, as Tobias, Mrs. Lovett's puppyish assistant, are the only cast members to make strong individual statements. But the company as a whole has a vivid ensemble impact, as perpetrators and victims, guilty and innocent.

As Todd commits his throat-slashing murders, a shrill whistle is heard, the stage is bathed in red light, and "blood" is poured into a bucket. Each victim then puts on a long white coat stained in red, which he or she wears for the rest of the evening.

As the dead mount, outnumbering the living, and the show moves hauntingly toward its end, with the storyteller put back in his straitjacket and again gagged, the stage tableau is haunting.

"Sweeney Todd" as written is compelling theater, probably the best-realized of all Sondheim's musical dramas. And much of the power of this production comes from the material.

Beyond that, its success is not that it's better than a traditional presentation of the show would be, but that it's daring - and effective. It takes us on a different theatrical journey; it gets us to see and appreciate "Sweeney Todd" from a new angle.