Once

"Complicated thing, this love," says a character late in "Once" - an observation that informs this bittersweet musical adapted from the 2008 Irish indie, which produced the Oscar-winning song "Falling Slowly." (A song so popular that a friend called it the Irish National Anthem.)

A story of love lost, found and reborn (but with a price), it is told by director John Tiffany in a beautifully modulated production. Like the current hit film "Inside Llewyn Davis," it uses folk/pop as its musical language, and, like that film, is a slow moving story about the recovery from grief. It may take some time before you fall for it, but by the end expect to be touched.

This, though, comes with a problem much bigger than this show itself, which started small, first in a workshop at the American Repertory Theater and then at the New York Theater Workshop, before finding its way to Broadway and a surprising Tony win for Best Musical two seasons ago. Call it musical scope creep. A show with this intimate scale would be better served at a much smaller space than the cavernous Opera House, where it is playing through January 19.

The production (as it does in New York), makes some concessions to being audience-friendly, including inviting audience members to come onto the stage before hand for an impromptu jam session with the members of the cast, who all double as musicians. It's a great idea, though you couldn't help but wonder if you're sitting in the balcony that you might miss half of the first act in getting back to your seat as the show begins.

Okay, that's an exaggeration, but does point out a conundrum that producers face when bringing shows such as this (and the current "Peter and the Starcatcher") on the road: how do you take a small-scaled show and play it in an oversized house? Even from an excellent seat not far from the stage, lines and lyrics were muffled, and a number of the performances felt heightened to fill the hall, turning characters into caricatures. At times, it felt like a mumblecore musical. More efficient sound design might help, and a smart stage manager may be able to bring the performances down a notch; but those are more cosmetic fixes that don't lessen the overriding problem.

That said, there's a quiet intensity to Enda Walsh's adaptation, which tells the story of Guy, a young musician's recovery from heartbreak through the help of a young woman he meets on the street. He's at the end of his rope as the show begins, singing what's to be his last song as he abandons his guitar on the street and heading back to his dead-end job (fixing vacuums in his father's shop). A young woman (simply named Girl) hears him and feels his pain; she also, magically, connects with him by producing a vacuum that needs fixing. Both are broken Millennials: she's a Czech expatriate living in Dublin in a troubled, long-distance marriage; he's a struggling busker willing to throw away his passion after his girlfriend abandons him for another and moves to New York. Romance sparks between the two, but their realities (including her young daughter, mother and extended family of Czech expatriates) intercede.

Instead she focuses on Guy's talents as a songwriter and musician, and sets out to develop his career. There is a romantic spark between the two, but they both downplay it, despite advice from family and friends. The irony is that because neither can let go of their past, they can't move onto embrace the present. Even Guy's songs are something of a cycle about his failed romance. With so much baggage, how can they connect romantically?

They do collaborate on a recording session, which re-energizes Guy to return to his music. The effect is infectious and other connections are made amongst those brought together at the session, which gives the thin story a bit more context. The story expresses the angst of first love with delicacy and humor, which is cannily augmented by Glen Hansard and Mark�ta Irglov�'s songs (most from the film).

What saves the show from being a precious exercise is self-absorption is the staging by Tiffany, which is both economic and organic. At first, the movement seems jarring and self-conscious; but after a moment, makes perfect sense. Like the songs, it extends the emotions, doing so with simplicity and emotional power. The result isn't so much a musical in a traditional sense, but a play with expressive music.

The cast, comprised of actors/musicians, is most appealing, though Dani De Waal felt a bit one-note as the musician's muse. In that role Stuart Ward believably captures the melancholy of unrequited love. He is also a dynamic performer that makes you believe he could have a career beyond busking on the Dublin streets. If only they weren't faced with the challenge of performing in this barn of a theater -- a place better suited for 'Wicked" than this small-scaled musical with broken-hearted protagonists and heartfelt melodies.

"Once" continues through January 19, 2014 at the Boston Opera House, 539 Washington Street, Boston, MA 02111. For more information, the Broadway in Boston website.