Unlike most of the opinions here I surprisingly enjoyed...I'd rather say LOVED this drama !! The whole drama was not perfect I have to admit but I found it lovely. The reasons are:

???? The Actors: The casting was well chosen (especially for the young actors).
I really loved Woo Do Hwan and Joy's chemistry. I was so emotional every time I saw them together in the drama (I screamed, laughed, giggled). Their relationship was so cute ! The other characters like Se Joo and Soo Ji were also touching, I could not hate them even when they did wrong. And Damn they are all good-looking folks!
(I did not really enjoyed the parents but they were ok. )

???? The Music: I really enjoyed the drama's OST ! It always made me in a good mood and DK's song...so touching <3 <3
The classical music used for the background was conceptual and contributed to the overall atmosphere of the drama.

???? The plot itself is not faithful to the original novel but they managed to create something quite interesting. I often got bored when I saw the parents/adults on the screen but the young adults' parts always captivated me. The drama was a bit long and the end was rushed. I am a bit disappointed that there is no real future for the team Soo Ji, Se Joo, Si Hyun. And even if there is a happy ending for the main couple, I wanted to see more (like a hug or how they would live together after 5 years) !!

Even with these critics I still plan to rewatch it in a few months or years because I really enjoyed the actors' chemistry and the overall mood of the drama! I really spent good times watching this drama, so I'll definitely watch it again !