After reading a lot of negative comments on this drama I felt obliged to write about it myself because I don't think the series was that bad at all. I have to note that this also wasn't my favourite series but I don't really agree with the ratings I have seen a lot of people give it.

Story
Though I have to admit the story was far from the best I have ever seen, it was still quite enjoyable. I don't agree that it was necessarily all over the place but rather the story could have been a lot more than how it eventually turned out to be. Everything seemed to build up to some great secret(s), but they didn't let the suspense go on until the last episodes and instead revealed most shocking things during episode 29-30, which made the last two episodes feel more like filler.
Also on a side note, I feel like the character Sung Joong was written very poorly. At first it felt like he would have a dark side as well, but throughout the series he continued to only be (unrealistically) nice and sweet.

Acting/Cast
One aspact which made watching this series difficult were the main leads, and if it hadn't been for Gikwang I don't think I would've continued the series. I barely felt chemistry between the main leads and though kdramas can be notorious for bad kissing scenes, these must have been the worst.
*Just thinking back about the elevator kissing scene makes me shiver*
However, the awkwardness seemed to reduce a bit while the drama continued and I was actually quite content with the others actors, especially Ham Eun Yong, who played Shin Yoo Na and Lee Gikwang, who played Sung Joong.
Another thing that I did enjoy was the way Eul Soon was styled. Though I was very annoyed with her hair constantly hanging in front of her face in the first episodes, you could see her grown into a more confident person in the way she started to dress, how she styled her hair and even 'started' to wear make-up at some point. Although she was ofcourse wearing make-up for the drama, she didn't have this fake 'no make-up look' where the actress is obviously still wearing a lot of eyeliner, lipstick and looks like she just came back from a hair salon while in the series she is supposed to look like she just had a bad night of sleep. Therefore I want to compliment the stylists and make-up artists of this drama!

Music
I don't really have anything special to note on the music. This series didn't have the most spectacularor memorable osts I have ever come across, but they were still enjoyable.

Rewatch Value
I don't think I'll ever rewatch the series, perhaps only for the scenes Gikwang was in because his character was just extremely cute.