This is the tender little acoustic romance that kicked the hell out of bigger, brasher shows at New York’s Tony awards. And it is easy to see why. Once is based on the Oscar-winning Dublin-set film and uses the same, sometimes devastatingly beautiful soundtrack composed by Glen Hansard, of the indie band, Frames, and Marketa Irglová. Not only that, the music, played superbly well by a the 12-strong cast of actor musicians, is attached to a gratuitously romantic Girl (Zrinka Cviteši) meets Guy (Declan Bennett) story.

Dubliner Guy fixes vacuum cleaners with his widower father. But it is his music that defines him and when Czech Girl walks into a pub to find him singing desolately about the ex-girlfriend who left him, Girl knows that she must save both man and music. For somehow she has gleaned that even though she has just watched guitar man Guy strumming until his fingers practically bleed — and singing to the point where his heart almost bursts, — he is on the verge of metaphorically killing himself by giving up music for good. And so the two end up making beautiful music together.

If the above description has a whiff of cynicism, it is because despite the sardonic wit injected into the story by normally dark-as-pitch playwright Enda Walsh, the love story on which the show rests is pretty thin, despite the fact that Walsh has fleshed it out. It’s a kind of Brief Encounter-lite plot, only without any sense of the social mores that keep Guy and Girl apart.

The musical has been called revolutionary. Well, it is innovative perhaps. Director John Tiffany’s masterstroke is to set the action in a cosy Dublin boozer that hosts impromptu gigs. Before the show starts, audience members are free to join the jamming cast on stage for a few jars.

Tiffany and choreographer Steven Hoggett revive some of the movement magic that informed their production of Black Watch, which was about the army regiment’s tour of Iraq. Heads tilt, limbs arc through the air and hands speak their own sign language.

It works very well here, though has none of the poleaxing impact it had in Black Watch, where the movement served as a way into the emotions of soldiers who had no vocabulary to express them. So there is an element of schtick being resurrected, albeit effectively.

There is also nothing much revolutionary about the score. It’s neither plot-driven in the old-school way, nor is it rooted in the internal life of the show’s character’s in the way the truly ground-breaking Spring Awakening achieved. Rather the songs here — including the Oscar-winning number Falling Slowly — are drawn from Guy’s back catalogue and romantic history.

There is though no resisting great songs beautifully sung; a love story - however thin - well told; and a hugely talented cast lead by the piano-playing Cviteši and guitar man Bennett, who are astoundingly on song.