As with parents and their children, critics really shouldn’t have favorites when it comes to the shows they see. But I admit it: Sweeney Todd, which just opened at Asolo Rep, is one of mine.

It’s just a pretty perfect and unique combination of so many things. There’s the setting: grimy, foggy, Victorian-era London. There are the characters: archetypes springing from penny dreadful tales that yet somehow take shape as real human beings. There’s the music: some of Stephen Sondheim’s best ever, surely; and there’s the story, which can move from the comic to the tragic to the horrific in seconds and sometimes be all three at once.

For these reasons, and also perhaps through good luck, I’ve never seen a less than successful production of the show. And the one onstage at the Mertz Theatre, under the direction of Peter Rothstein, who also helmed last year’s Ragtime there, does not break the chain.

As he did with Ragtime, Rothstein focuses the show in a more intimate than spectacular way, with fewer cast members and musicians, allowing most actors to double roles as citizens of London when it’s called for. When the curtain went up on opening night, I was at first concerned that the dramatic power of the mood-setting “The Ballad of Sweeney Todd” was diminished due to fewer voices, and the zombielike movements of the actors took me aback. Perhaps the audience was still settling in, and viewer concentration, too.

But those concerns were swiftly put aside. Once Sweeney (Allen Fitzpatrick), the former barber Benjamin Barker (say that three times fast), rises up in vengeful mode, the story moves enthrallingly and inexorably along.

Sweeney has reasons aplenty for wanting revenge, after being sentenced unjustly to a life term in Australia by a judge who lusted after the barber’s innocent wife. His escape, thanks in part to the good-hearted sailor Anthony (Perry Sherman), brings him back to London—a cesspool to him, where the rich and powerful keep the poor in their lowly place.

But revenge, of course, has its pitfalls, as he’ll painfully learn. In the meantime, he discovers that his lovely young daughter, Johanna (Elizabeth Hawkinson), is the wicked judge’s ward, and that his former neighbor, Mrs. Lovett (Sally Wingert), has kept his sharp, gleaming razors ready for him. Woe betide Sweeney’s unsuspecting customers.

Playing out on a set (by Kate Sutton-Johnson) that allows for something of a neglected carnival feel (pre-curtain music reinforces that), the dark, grimly funny story takes us from city street to sitting room to madhouse, with a cast of just 10 ably bringing to life the seamier sides of the metropolis. Fitzpatrick is a compelling figure as the obsessed Sweeney, a hero/villain whose own doom seems foretold from the beginning.

But he also has his more frolicsome moments with Wingert, excellent as the conniving Mrs. Lovett, especially when they first conceive the plan for making those delicious meat pies on “A Little Priest,” or when she takes to a swing on the wishful “By the Sea.” Wingert’s voice may strain occasionally on high notes, but it’s more important here that she brings together the humorous and awful aspects of her character, and she does that in spades.

The voices of Hawkinson and Sherman combine beautifully on some of Sondheim’s more romantic duets, and Evan Tyler Wilson (wearing an appropriately clownish costume by Alice Louise Frederickson) scores fine comic moments as competing barber Pirelli. David Darrow is older than the boy Tobias, whom Mrs. Lovett takes under her wing, is sometimes played, but you can clearly see the damaged child inside, and his number with her, “Not While I’m Around,” is a highlight.

Rothstein’s choreography is as fresh and imaginative as his direction. And Paul Whitaker’s lighting, whether gloomy or explosive, as at certain key moments, serves the tale of the Demon Barber of Fleet Street well.

Sweeney Todd continues through June 1; for tickets call 351-8000 or go to asolorep.org.