The title Happiness is an ironic one: the series is set a little after COVID-19 has become controlled, but with a new rabies-like syndrome spreading. How Patient Zero was created was never identified, but it was identified that a virus that functions largely like the rabies virus slowly transforms people into feral zombies that thirst for human blood. One novelty of the series is that instead of hydrophobia (or fear of water), people afflicted with the virus suffer from excessive thirst. Once they turn and taste blood, however, it becomes only a matter of time before they are overrun by the virus; if the virus reaches the brainstem, the patient becomes terminal as there's no cure discovered yet with the onset of the series.

I think that the series as a high-concept thriller performed reasonably well, except that its early episodes had struggles with characterization: for instance, Yoon Sae-bom, despite being a member of the Special Operations Unit, was being careless and even put people in danger despite her training. Her impulsiveness had brought quite a few people at risk, and her gung-ho attitude would have resulted to her demise had she not been counterbalanced by the cerebral yet placid Yi-hyun.

I do admire how the CDC chief, Han Tae-seok, was written. His efficient and highly rational actions saved a lot of people's lives because he was quick with lockdown procedures and even killing those who had become terminal in order to limit the spread of the virus. In fact, the lockdown that occurred within Seyang Forest was because of him: after he had established that one of the side effects of the medicine they had been selling before was the rabies-like syndrome, and that it had been sold in the apartment, he immediately locked it down.

Because of the lack of supplies, however, the apartment tenants have to fend for themselves, and this is where their personalities are laid-bare. Most tenants are selfish, but there are a few like the lead couple who show their grit and kindness consistently. In fact, one of the series's high points is how it has seamlessly written into a thriller one of the healthiest romances in K-drama.

Because both have been trained in high-pressure situations, Yi-hyun and Sae-bom never lose their humanity, even with those infected within. They try to maintain order, provide equitable distribution of food and water, and try their best to protect the other tenants from the infected without. However, because "hell is other people," selfish tenants willingly put other people at risk, and even lead a few to be infected or killed.

As a viewer I approve how they wrote the disease. Even their treatment modalities toward the novel disease were sensible. One major plot hole that I think wasn't adequately resolved were the children playing outside despite the lockdown in their apartments. I thought that was inconsistent with the accuracy with how Han Tae-seok implemented pandemic control principles, as social congregation should be minimized in these events, especially without a certain cure.

The final episode was also a bit underwhelming, although I loved how it magnified the toughness of the relationship between the married couple. As a fan of romance, I also enjoyed the culmination of the love that percolated for years. Outside these minor nitpicks, however, Happiness is a great and enjoyable thriller anchored by one of the healthiest romances this year. Recommended.