I didn't watch the drama while it was airing because high school dramas are not my thing. But I decided to give it a try because of how popular and liked it was. And I don't regret it!

In a way, it is your typical high school romance but the fact that the drama plays with the usual tropes while being critical of them makes it more enjoyable.
One of its strong points is Eun Dan-Oh's character : she is very likeable. First, the fact that she apprehends her situation with humour: I especially enjoyed her disgust at some of the dialogues during the ''stages'', it was one of my favorite things all along the drama. I also liked how she stays upbeat and optimistic even when she appears helpless and her situation hopeless.
I liked that some of the characters were deeper than I expected, especially Baek Kyung. He makes the story not so black or white. He is the mean guy but one who is confused and searching for his own self. I think his character embodies how many feel at his age : you are behaving the way that is expected of you but questionning your identity, trying to find what you really like and who you want to be.
I liked Haru. I agree that his character is not well developped but I find it nice, for once in a drama, that the male lead exists only for the female lead... I liked that his character is calm but not cold and indifferent as this type of character tends to be.

The thing that makes this drama not so perfect is the inconsistency. First, in the rythm of the drama : the first episodes are really good and grab your attention quickly as does the end but the second half gets slow and draggy. Then, there is the acting. I still don't know if it is Kim Hye-Yoon's acting or Eun Dan-Oh's character that is not well framed but I found that there were many moments where I was not convinced by the portrayal of the character. Her demeanor was sometimes too different from what I think Eun Dan-Oh is supposed to be. Especially during the romantic scenes. The last thing that bothered me is the editing. I liked how they incorporated manga effects into the editing. I found the shift between the stages and the shadow to be such a good idea, But why couldn't they use all the different effects throughout the whole drama?

Finally, this is a great high school romance drama. You will get the usual clichés but with a twist. The story is deeper, more complex and the lead characters are refreshing.