They are both working odd jobs to pursue their true calling, which is music. And the music they perform throughout the film is absolutely perfect. All of the songs are originally composed and performed by the two leads and that is for good reason. To describe how good the music in the film is, I will just say that there is not one song in the movie that I wouldn't want to listen to again.
John Carney does such a brilliant job of not over-directing. It would've been easy for him to try to do too much with such talented musicians, but he makes the right decision by letting Hansard and Irglová do most of the work. He realized how good they were together and let them steal the show. It is a smart film that knows what its purpose is and never strays off course.
There is not much more I can say about the film in this review other than you just have to see it. And if you have seen it, give it another viewing. In a running time of only about 80 minutes, this movie has so much to like and absolutely nothing to hate. I dare anyone to come out of this film not humming the music and not feeling better about themselves. It is a movie that simply makes you smile. It's tough to compare it to the bigger, darker films of 2007 such as No Country for Old Men, There Will Be Blood, and Michael Clayton, but this is a film that is just as satisfying, if not more satisfying than all three I just mentioned. I'm probably beginning to sound like a broken record, so I'll just stop at this: Once is one of the best films of 2007.