Once is a paean to the power of music, and the celebration begins well before the official curtain time, with an on-stage pre-show in which the members of the ensemble—who supply ALL of the show's music, vocally and on a variety of (mostly string) instruments—each get a chance to strut their stuff and cut the rug a little, too. A dinner engagement kept me from getting to the theatre until nearly 8 o'clock; don't make that mistake.

This informal olio, performed on the show's welcoming pub set (designed, with the costumes, by Bob Crowley, at the top of his form), segues subtly and masterfully into the play proper, with the arrival onstage of Steve Kazee, who plays "Guy," the protagonist of Once, singing a lovely ballad called "Leave." As the stage clears, Cristin Milioti, as "Girl," appears, and as we watch her listen we know that something special is about to happen.

And it does: the first act of Once is a blissful fairy tale, propelled by music and people's love/need for it. Guy is about to abandon his guitar and his singing and songwriting, but Girl won't allow it. She insists instead on a trade—she will play a song for him (a piece by Mendelssohn, on the piano at the music shop where she works) if he will fix her broken vacuum cleaner (which is rolled onstage, incongruously, by one of the ensemble members, a portent of the whimsical magic to come). Next, Girl convinces Guy to share more of his own music with her, and before he knows it she's not only concocted a plan to make him famous in New York City but also set it in motion. The story is pushed forward by a succession of songs, notably "Falling Slowly," the Academy Award-winning tune from the film of the same name, on which this show is based. Girl and Guy are falling in love, and we are too, with both of them.

The fact that both of them have others with prior claims on them far from the city of Dublin where Once takes place gives us a hint that the fairy tale may not conclude the way we'd like. This is, finally, a bittersweet tale, and I was disappointed that so much heavy plot development dominates its second act, as if the show's creators had forgotten their theme of music's potency in our lives. Once could use a song or two more as it moves toward its end.

But this does not finally detract too much from the charm of the piece overall. The songs, mostly by Glen Hansard and Markéta Irglová, are lovely and often exciting, and they are gorgeously played by the company under the direction of Martin Lowe. John Tiffany's direction and Steven Hoggett's movement serve the story mightily; Enda Walsh's book, from John Carney's screenplay, is very effective until it bogs down near the finish. The performers are terrific, with Milioti simply stunning as the winsome, determined, charismatic, and complicated Girl and Kazee virtuosic on vocals and guitars nearly non-stop as Guy. Everyone in the ensemble gets at least one moment to shine, and all must be acknowledged here: David Abeles, Will Connolly, Elizabeth A. Davis, David Patrick Kelly, Anne L. Nathan, Lucas Papaelias, Andy Taylor, Erikka Walsh, Paul Whitty, and J. Michael Zygo. (Two young actresses, Ripley Sobo and Mckayla Twiggs, alternate as Girl's daughter Ivanka; unfortunately no indication was made in the program as to which of them I saw.)

I had a delightful time at Once. I particularly loved that, bucking what seems to be the new norm for Broadway musicals, this show is content to let us come to it and discover its charms for ourselves, rather than trying to beat its audience into submission with abundant noise and production value and relentless hyperactivity. There's a sweet, aching heart at the center of this show, and I appreciated listening to its never-drowned-out beat.