How far Stephen Sondheim has come. “Follies,” widely seen as problematic at its 1971 premiere, is now a classic, headed back to Broadway in a star-studded Kennedy Center production. And “Sweeney Todd,” once a provocative Gothic horror, is now family entertainment, suitable for spectacle treatment at Wolf Trap, where it played in the sweltering heat of Friday night.

“Sweeney Todd” is, for me, Sondheim’s most effective work — its Grand Guignol caricature rings somehow truer than the forced interpersonal relationships of some of his other works — but it’s a challenge to bring it across in an outdoor setting, where the chirping of crickets mitigates its horror. At Wolf Trap, the challenge was furthered by miking that kept muting the ensemble and sent up occasional whines of feedback to compete with the score’s chilling factory whistle.

But the piece is strong enough, and the singers did well enough, to mainly carry it off. They deserve particular praise for their impressive diction (not always a strength of operatically trained artists), measurable by the number of times the laugh lines actually got laughs.

Margaret Gawrysiak’s Mrs. Lovett particularly shone in this regard. This role of the purveyor of meat pies made from the bodies of Todd’s victims is so often given to non-singing character actresses — Angela Lansbury, Helena Bonham Carter — that it’s a treat to hear it done by a real singer. Gawrysiak — backed by experienced conductor Larry Blank, who offered reasonably efficient leadership of the National Symphony Orchestra on Friday — took her music a bit slower than the ideal and flagged toward the end of the evening’s showpiece, “A Little Priest,” but offered compensation with an amusing performance and a hefty, easy and sweet sound.

Not everyone dealt as successfully with the Broadway score. As Todd, Michael Anthony McGee showed that a role that sits in the lower middle of the voice and calls for a lot of discursive singing can challenge an opera singer; he sometimes sounded constricted, though he maintained a glowering presence.

Johanna, Todd’s innocent teenage daughter, is the role you’d think the Wolf Trap Opera, a program designed to give experience to young professionals, would have the easiest time filling, but Ashlyn Rust showed all the worst foibles of operatic training, sounding thick and a little overdone, not quite clearly on pitch, and as if she felt a lot of extra things had to be done to the music at all times.

As Anthony, the young sailor who falls in love with her, Eric Barry showed the kind of straightforward, honest singing that best serves these particular ingenue parts. Edward Mout’s Toby was even stronger; he gave a beautifully unfussy account of “Not While I’m Around,” which in my book may be Sondheim’s most successful romantic ballad, perhaps precisely because it’s written to be sung by a half-stunted child-man expressing his tenderness for a murderess.

Many singers, though, had trouble finding their way to a less operatic approach. Kenneth Kellogg’s Judge Turpin was not as on the mark as his firm, dark voice indicated it would be, perhaps in part because of the awkwardness of his one aria, which involves self-flagellation and erotic climax and is awfully hard to tone down for a family audience (though this production found a way to avoid the starkness of the rape scene, indicating it with euphemistic dance gestures instead). As Pirelli, Nathaniel Peake fell into the trap of overdoing a role that is already overdone. And Lindsay Ammann’s Beggar Woman got so manic that it was often hard to understand her.

Tara Faircloth’s production was advertised as a full staging but didn’t quite feel that way. S. Katy Tucker’s videos wafted across a screen above the players’ heads, showing outlines of London, half-realized interiors and plenty of fire and smoke; red chairs in various configurations served as props; and Todd’s victims, once killed, immediately stood up and took off their tops to reveal white shirts or shifts drenched in blood. This sense of anticlimax was something of a hallmark of the evening, from which, nonetheless, Sondheim fanciers were happy to extract the exceptional pleasures.