I believe this is the fourth or fifth film I've watched starring Min-Sik Choi, who is quite an accomplished actor. The DVD cover proclaims Happy End to be "one of the most controversial Korean films ever made!" It's not difficult to imagine why this film might cause controversy. On the one hand, shortly after the film begins, a semi-explicit sex scene takes place that seems to go on for a gratuitously long time. But nothing is shown during the sex scenes that wasn't shown in the much less controversial, more traditional Korean period piece, Chunhyang. Perhaps it is the nature of the sex taking place, that of illicit extramarital liaisons, that contributed to its controversy. But I believe the bulk of the film's controversy is due to what ultimately emerges as the film's theme.
This film could be viewed as a sadistic wet dream pandering to certain men who are disgruntled by what they feel is an emasculating and increasingly common situation of this modern age: that of the unemployed, stay-at-home husband. Except that when this unemployed husband is home, he spends most of his time watching soap operas, only occasionally lifting a finger to help with the baby. Instead of looking for work, he kills time each day crouched in the used book store, reading romance novels, to the chagrin of the store owner, whose policy regarding such patrons is less welcoming than that of Barnes & Noble. The husband is mopey, and never expresses affection towards or sexual attraction to his wife. Since he barely helps out around the house, when his wife gets home from work she ends up having to do the cleaning and the chores on top of her job, even though he has much more free time and is home much more than she is. As a companion, he is ineffectual and impotent. At one point during the final third of the film, as she's alone at home on her hands and knees scrubbing the floor, she tells herself that she has to "end it". It's unclear at the time whether she's talking about her relationship with her husband, or with her co-worker Il-bum. For the most part, she endures the imbalance in her relationship with her husband without much complaint, perhaps contritely due to a sense of guilt she possesses over the fact that she is engaged in an affair.
It's revealed that Il-Bum is actually baby Yun's father, and that they were a couple before her current husband came into her life and married her. Why would she leave her former lover to be with such a pathetic, and ultimately deranged and lethal man? There is an indication that at one time he was successful and financially more secure. But her past and present boyfriend is more attractive, more passionate, and more considerate. For reasons that aren't fully explained, she reacts negatively to his small, caring gestures. When he buys a toothbrush that she can use when she's over at his place, she lashes out. She does the same when she discovers toys that he's bought for the baby. She seems conflicted by emotions of desire, guilt, and annoyance with both the men in her life and her situation in general. There is also at least one major plot hole in this film that I could not overlook. At one point near the end of the film, she mixes a bit of sleeping medication into her baby's formula, so that she can leave her in the apartment to go confront her lover and break off their relationship. But her husband could come home at any minute, and yet she apparently doesn't stop to consider that. Perhaps the simple, though inadequate answer to the questions raised by her acts is that she just isn't a very sensible woman. But nor is she portrayed as being mentally slow. Distracted, certainly.
Inevitably, her husband comes home to find the baby there alone, and eventually discovers that he's being cheated on. He premeditates a vicious revenge, in which he terrifies her before committing brutal murder, bludgeoning her over and over with her lover's knife which he stole from the former's home, gradually slowing to pause and stare at the body for a couple moments in between stabs. He then uses the weapon to frame her lover for the murder he's committed. The last time we see Il-Bum is in custody, being pressured into giving up his right to remain silent without a lawyer. We're only left to imagine what becomes of him.
There's a misanthropic sense of self-satisfaction in the supposedly "clever" irony of the film's title. Not knowing what the filmmaker's intentions were, I'm led to wonder after watching this film if those who wrote and directed it consider the end which befell Bora and her child's true father to be a "happy" one. The superior tone of one of the previous comments here glibly indicates with a wink and a nod that she deserved to be horribly and brutally slayed by her baby's "touching motherly daddy" because SHE'D gone too far. How alarmingly vile.