Into The Woods, Linbury Studio, Royal Opera House, London

Time was when it was fashionable to suggest (though heaven knows why) that Sondheim wrote great first acts but failed to deliver in the second. Errant nonsense, of course, and nowhere more so than in Into the Woods. At the close of Act I, when all the "happily ever afters" point to a natural and satisfactory conclusion, you'll invariably overhear someone - inevitably, a first-timer - popping the question, "Is that it?". No, that is not it.

Perfectly self-contained though the first act may seem, it is only the beginning. Without the second act, the first is merely a trick - a slick one, it's true, but still a trick. And with this production, maybe because Will Tuckett's staging of that trick is not quite slick or quick enough to leave one breathless in anticipation of what follows, the whole evening doesn't quite gel - there isn't that "just when you thought it was safe to go back into the woods..." feeling. The second act isn't quite earned.

The point about Into the Woods is that, in the first act, the characters are familiar only from the jumble of fairy tales they inhabit; in Act II, they live and breathe and bleed and die. We start to see them as real; we start to care. Or we should.

Maybe Tuckett needed to find more of an angle, or, dare I say it, a concept. Richard Jones did for his London premiere. In any event, the long exposition of the show needs to be punchier and more incisive. Tuckett's cast is good and hard-working, and nobody should underestimate the technical difficulty of the material that they have to negotiate - it's a minefield.

Individually, they get through it largely unscathed, but collectively they don't have us catching our breath in disbelief at the virtuosity. Tuckett and his excellent designer Lez Brotherston give us smoke and mirrors, but insufficient mystery. Yes, the show looks magical, but is it unsettling enough? Brotherston creates a more or less traditional pop-up story-book look from sliding cut-out trees, but with naked light bulbs for stars and an omnipresent clock locked on to each passing midnight. Banks of mirrors play wondrous tricks with the light, but instead of closing the action in on itself, instead of at least alluding to the claustrophobia of characters growing increasingly "lost" on their sojourn into the woods, the mirrors actually open things up. There are few surprises, save the leaves showering the auditorium as the unseen giantess angrily stomps through it. The sky does quite literally and dramatically fall at one point, but, mostly, Tuckett leaves things to our imagination. Which I suppose is only fitting.

Certain performances inevitably stand out. Suzanne Toase is the most knowing, the most pubescent of Little Red Riding Hoods - plump and getting plumper from a few too many pilfered pastries. Don't mess with her. She doesn't just skin the wolf, she wears it. Then there's Clive Rowe and the talented Anna Francolini. As the Baker and his Wife, they both have their moments of truth, she secretly wishing that she was in a more romantic story, he finally finding strength in adversity with that wonderful Sondheim song, "No More".

The two princes, Nicholas Garrett and Nic Greenshields - lords a-leaping, both - earn the monopoly on masochism with their "Agony" duets, and Beverley Klein so brilliantly exhausts every last pantomime cliché with her picture-perfect Witch that you're almost sorry when she sheds the prosthetics. And, my goodness, she gives some welly (and pathos) to her "Last Midnight".

Gary Waldhorn is the storyteller, casually ambling through the action like he's heard it all before. He has, of course. It's still a stroke of genius when the book- writer James Lapine has him start questioning the characters' motivations. You half expect him to say: "Will the last person out of the woods please turn out the light."

To 30 June (020-7304 4000)