As we enter the Gaiety, we discover that Once has already begun: the cast are gathered in what looks like an ordinary pub where a session is underway. They play music for about twenty minutes while members of the audience wander onstage – ordering pints from the barman, listening to the music, waving to friends who have just arrived.

As we settle into our seats, we realise that Bob Crowley’s set is not an exact replica of a traditional Irish pub: along the walls, he has positioned a series of mirrors, of varying shapes and sizes. Those mirrors allow us to see the actors from different angles during the performance, but their more significant impact is to ensure that, throughout the evening, the audience will always be able to see itself reflected on-stage.

One of the young men in the bar is asked to sing: he plays the opening chords of a song called 'Leave', the lights gradually fade, and then a young woman walks from the auditorium onto the stage. Gradually we realise that we’ve just been introduced to the couple at the heart of Once: Guy (Declan Bennett) and Girl (Zrinka Cvitešić).

The impact of these introductory moments is profound: we’re being shown that the gap between stage and auditorium, between actor and audience, and between the real world and the performed one, is much more porous than we might have expected. Even before the show formally begins, then, the audience has been told something very important: Once is about us – our lives, our hopes, our feelings.

This is perhaps the best example of how director John Tiffany has set out to theatricalise John Carney’s 2006 movie, which famously won an Oscar for Glen Hansard and Markéta Irglová’s 'Falling Slowly'. That film appealed to audiences because of its restraint: relatively few words were spoken, and much of its emotional undercurrent was conveyed through close-ups on Hansard, who used grimaces and frowns to reveal the emotions that he couldn’t express through speech. This characterisation may have been an elegant way for Carney to manage the problem of filming a romance that starred two non-professional actors, but the effect of that strategy was to create a moving contrast between Hansard’s inarticulacy in speech and his eloquence as a musician. That contrast allowed us to understand that Guy sang not because he wanted to but because he had to.

The problem is that the theatre can’t use close-ups, and that silence is not really appropriate for a Broadway musical. Instead, Enda Walsh’s book fleshes out the two central characters, while adding humour, and substantially developing the supporting roles. This is indisputably an Enda Walsh script: we get a hilarious new song called ‘Abandoned in Bandon’ and a Cork vs. Dublin subplot that couldn’t have been written by anyone else. He also brings to the surface many of the feelings that went unexpressed in the movie, a decision which might reduce the emotional impact slightly, but which also means that we’re now watching a broader and richer range of human experiences.

Walsh also avoids making his characters seem too worthy or self-important: whatever pretensions they have will be undermined by characters like Aidan Kelly’s likeable music shop-owner. Indeed, one of the night’s strongest moments is an act of deflation. Shortly before the interval, Guy nervously steps onstage at a pub open mic night, and announces that he’s about to sing a song that he wrote himself. There’s silence for a moment before one of the characters quietly mutters – in a tone of utter abjection – one word: “fuuuuck”. Walsh has affection for Guy, but he knows that sometimes there can be nothing worse than listening to a young man with a broken heart and an acoustic guitar. Yet he then builds us back up again by having Guy sing the song 'Gold', which – in terms of movement, instrumentation, and vocal delivery – results in one of the strongest and most moving ensemble performances of the evening.

Once comes to Dublin from New York en route to the West End, so Irish audiences may wonder how relevant the production is to this country. The performances are generally very good, especially from the two leads, but I did notice people around me flinching occasionally when the Irish accents seemed to wander (and I would guess that any Czechs in the audience might have similar cause for complaint). Yet this is a musical that can speak directly to an Irish audience.

In particular, Walsh seems to want to address directly the state of the country today. Carney’s Once was made at a time when the Celtic Tiger was still booming: the idea that Ireland might be a land of opportunity for Czech immigrants was much stronger in the film than it is in the musical. Now Walsh’s characters express much more uncertainty and ambivalence about our country, asking whether it’s possible to take pride in Ireland any more. They decide on a positive answer to that question, but it’s notable that they feel the need to think about it for so long.

There is therefore an interesting – and sobering – parallel between the script and the production’s journey from America to the UK. At the end of the action, Guy leaves Ireland, as in the film. But now there’s a much stronger sense that his departure is (in both senses of the phrase) for good, that Ireland can’t offer him the success and recognition that he needs and deserves. I was struck by the parallel between Guy’s departure from Ireland and the fact that this very Irish story – which features such talented Irish artists as Enda Walsh, Bob Crowley, Glen Hansard and Aidan Kelly (together with many excellent international artists) – originated abroad, and that its all-too-short production in Dublin is, essentially, a warm-up for the West End run. This is in no way a criticism of the show or its producers, but I found very poignant the realisation that many Irish theatre-goers will only be able to see Once if (like Guy) they leave Ireland.

All that said, Walsh doesn’t want to leave us feeling hopeless. One of his most telling interventions is a passage in which Girl reminds a bank manager of the importance of adequate funding for culture, saying that the arts can show the world that Ireland is still “open for business”. He also reminds us that, despite the gloom, there is still much to love about this place. The vitality of Irish culture is made evident is many ways in the production, most effectively in the staging style adopted by Tiffany. Because all the action happens in a pub, the show is like a theatricalised version of a night out in an Irish country local, in which everyone is expected to perform a party-piece. Walsh’s debts to The Weir and Conversations on a Homecoming are not too difficult to detect.

And while the story of thwarted love gives the show universal impact, Once is also a love-song of sorts to Dublin, offering us the promise that we can have hope for the future, even if the only thing we have left is hope. So at the end we are invited to look again at ourselves, our lives, and our city. Are we really prepared to believe that love, hope, community, art and music can be enough to see us through these bad times, as the show seems to suggest?

Well… Maybe just this once.

Patrick Lonergan teaches Drama at NUI Galway. His most recent book is The Theatre and Films of Martin McDonagh, which is published by Methuen Drama.