One thing that makes Once wonderful is how prickly The Guy (Glen Hansard) is to The Girl (Markéta Irglová) when they first meet.
Writer-director John Carney can be read as playing with the “meet cute” convention of romantic comedy in the initial scenes between Guy and Girl. The first subversion of form is in how the two encounter each other. Classically, circumstances contrive or conspire to bring the romantic protagonists together and into close, intimate contact by, say, making them share the last seat on a bus or the trunk of a car. Here nothing in particular brings Guy and Girl together. She notices him in the course of daily life and then, in a further break with convention, makes an affirmative choice to approach him. There is no fated coincidence at work (I do think that the happenstance of the vacuum cleaner is a nod and wink at the idea that the two leads are “meant to be”).
Typically, upon meeting, romantic leads will undergo an alchemical reaction to each other. It may initially explode in disdain, but the slow burn towards love will have begun. Indeed, in many cases the disdain is certainly feigned. In Once, she is certainly drawn to him, but through his music, not some ineffable chemistry. He is wary about her, holding her at a distance, treating her as the stranger she is and acting as the emotionally fragile person he is. However, his prickliness and her earnestness simply serve to defer, not erase, their alchemical moment, which happens when they first play music together. The twist in this case is that Girl and Guy actually do have a bond, but they have to discover it. It isn't just there in the air between them.
The familiar but strange quality of Guy and Girl's meeting cute sets the audience up for the unexpected. In a traditional romantic comedy, you know that the two leads will end up together, that's part of the pleasure in the genre. But in Once you're not even sure if “Will they end up together?” or “Will they or won't they?” are even the right questions. Wonderful.