I like the story and all the actors with their roles, except Jin ki joo (sorry, nothing personal), she doesn't match Park hae joon. I just dont see they're good together. She's good, but maybe for different role.
It reminds me with the drama "TOUCH", where male and female main actors dont match each other. Ended up with NO IMPRESSION after watching it.
I dont know how they did the casting in choosing the actors. It's not ONLY the capability of acting, but the Look should be considered, according to the story, and possibility of "how the audiences will see it".