The comedic first two acts work alright, and the drama in the final act is solid, but they're just not meshed together very well. Balancing comedy with drama is something Yoji Yamada would master with the Tora-san series, but not so much here - maybe it's that the drama is a little too intense, clashing with the very broad, kind of slapstick-heavy comedy.
Speaking of Tora-san, there's a film in that series which has a similar title to this, called Tora-san's Song of Love. I have no commentary on that or anything insightful to add (I don't remember that one specifically) - I guess it's just a neat coincidence and/or observation.