This drama would have been a good horror mystery if the lukewarm-lame romance were removed from it. I would have preferred that the ML stayed cold, arrogant yet strong and over-confident throughout the drama. While I was watching this drama, I find myself shouting often at the TV screen to tell the characters to keep on running or escaping or not waste time during suspenseful scenes because of the imminent dangers around their corners. There are crazy Japanese soldiers or monster running around all over the dark places! And yet, those people were busy either talking trash, or arguing or crying or just making googly eyes at each other (yes, the ML & FL) trying to foster some fake romantic vibes for the drama! There's no feeling of urgency about the danger or fear. No tension or suspense. It's like the main characters knew they were super human, they have great plot armour and they know they will survive.
Compared this with Train to Busan drama, this new drama is as scary as some B-grade Hollywood Halloween film. Even the Korean "Kingdom" historical zombie horror-drama is 2x better. LOL... hehehe...
Anyways, this is only my opinion (plus my sister's too as we watched it together).