Sweeney Todd, Royal Festival Hall, London

The final image of David Freeman's concert staging of Sondheim and Wheeler's Sweeney Todd at the Royal Festival Hall has the entire company eyeball the audience and draw razors across their throats. We could all be Sweeney, they would seem to be saying. What's your moral compass? It's a chilling touch. And the evening provides a few of those: like what dear Nellie Lovett, Sweeney's ever hopeful helpmate, might do with a hostess trolley, a hacksaw, and a handful of bin liners. As Sweeney says to the Beadle: "I am, Sir, entirely at your disposal."

Sondheim's masterpiece has come at us in a number of forms, ranging from full-blown operatic to the thoroughly deconstructed. Like all masterpieces it's very accommodating. But I'm not sure it entirely won its battle with the Royal Festival Hall. There were two main problems with this concert staging. One was the question of just how far you go in terms of the action; the other, more critical, was the sound. After John Doyle's DIY handful-of-instruments approach at the Watermill in 2004, it was good hearing this most filmic and symphonic of scores in all its Grand Guignol glory. But despite conductor Stephen Barlow's best efforts, even a cut-down London Philharmonic proved tricky to tame in this newly enlivened acoustic. That required far more sophisticated sound design than was in evidence here. Too much orchestra, not enough voice, seemed to be the general consensus.

Still, it's amazing how the ears adjust, and with a cast this talented and a director this quick to make the point that in terms of its weather and attitude to the homeless London may not have changed as much as we would like, there was a modicum of chill in the air from the very start.

The terraced stage area was oddly laid out, with the orchestra squeezed into the left-hand corner and acres of open space with props hidden under black shrouds. Hidden, too, were the emerging principals, with Freeman again rather cleverly losing them in the black anonymity of the crowd until fate throws them into the foreground.

It's hard hiding Bryn Terfel but hide him they did until Sweeney's amazing entrance. And right from the start he was everyman turned psychopath, eyes bulging with resentment, revenge and only revenge on his mind. Vocally and physically he was big, he was scary. But scary because of the extremes he chose to draw between the booming melodrama and a cold, calculated understatement. The explosiveness of his "Epiphany", which had him striding into the front stalls hungry for new customers, provided a close shave for all those in his proximity.

He barely noticed Mrs. Lovett the entire evening – except, of course, when he needed her. And Maria Friedman, emerging from her shroud like a superannuated Minnie Mouse in a red polka-dot frock, was hard to miss. What a smashing performance this was and how good it would be to see it develop in the theatre. Whether stomping on bugs, bagging body parts, or drooling over Mr Todd, Friedman deployed her best Barbara Windsor-cum-Marie Lloyd belter voice with attitude. The miking might have helped her a little more, but she and Sweeney's music hall turn "Have a Little Priest" – a grisly catalogue of who exactly they might pop into their pies – certainly hit the spot.

So did other performances: Daniel Evans's terrifically vital and verbally dextrous Tobias, Adrian Thompson's cartoonish Pirelli, Daniel Boys' sweetly sung Anthony, and Philip Quast's odious Judge Turpin. That first moment when Sweeney has him in the chair, relishing the prospect of slicing through his jugular, was played out here in sensuous and suspenseful slow motion. And yes, it was scary just how much we shared in Sweeney's pleasure.