The reviewer who complained about the romance subplot is so off it's wild.
First of all, this show's actual genre is crime romance. It's listed as a romance. So why would they expect there not to be a romance. And the romance itself is a slow burn and is given way less screen time than the crime and horror aspects.
Second, the male lead's character arc is completely tied in with the overall plot arc and with FLs character arc, he's not just there to look pretty or make us swoon, he is very important to every aspect of the story and drives much of the action. He doesn't just pop in to be romantic, he is key to the central plot of the serial killer and is the reason why the FL even has a character arc, cause...
Third, the FL is not a judge trying to advance her career, she's a demon trying to complete a mission. She's there for one job and one job only -- to find and kill murderers to send them to hell. The ML is not distracting some story of a judge trying to become a better judge, he's making her interesting by being the key to her humanizing as a demon, which is the entire central point of her character arc. Watching a demon go around coldly killing murderer after murderer with no change would get real boring after a few eps.
It seems that reviewer just wanted a completely different story, with different characters and a different plot. Instead of looking at what story this show is trying to actually tell, and if it's doing a good job.
Which, it really is. This show has so much going for it and the romance only adds to that. The FL and ML have fantastic chemistry. The writing is very tight and knew where it was going from the start, everything connects well together and develops so organically. Good directing a great editing. All the actors are nailing their roles. It's fun at times, scary at times, moving at times. It's been my favorite drama this year.