I loved this show. Though I had to watch it more than once to better understand the story, I loved the comedic tone. It completely balanced with the scenes that were emotional and quite serious. This was especially necessary because the serial killer in the show was written in such a sadistic way.
I especially loved the romantic chemistry between Park Bo Young and Park Hyung Shik. Their chemistry made the story seem more real and fluid; it also helped to differentiate the reasons why Park Bo Young's character made the romantic choices she did throughout the series. It took me two viewings of the show to understand the love triangle, so if you have trouble I would suggest re-watching the show to better understand.
FYI: I loved the grandmother the best. Her role in the show was a small one but she was very memorable.