This one of the best c-dramas I have ever seen. The acting is just perfect for what they are portraying. The story is written in a way that if you watch it, you have that feeling of it's not too slow nor too fast. For a whopping 36 EPs it felt surprisingly short as I've fallen really in love with the characters. So all in all I can only say that it's all about the people in this drama and how they're played, written and shot (the camera work). Props to everyone in this drama, but the FL and ML stood out because of their chemistry.
Thus far, I've not watched many c-dramas, but most of the time I encounter one problem: How they're acting and how the story is written. Most of the time, the dramas tend to be very plain. But this one (at least for me) has shown that if you give the right people a budget, get a good written script and to get people who show their chemistry believably you can get this drama.