First of all the casting done is so perfect from the main leads to the second to all the supporting characters and even the cameos, they all are bang on perfect. The story was beautifully written and very cute. One thing which makes it more interesting is the North Korean background and the details which they have looked into purely loved them.
The chemistry between the Main leads as well as the second leads were perfect. Aaah how can I forget the breathtaking beautiful swiss scenes! The supporting characters couldn't have been better than this. I loved almost everything of this drama it was beautifully and ended without haste.

One thing which I personally would have loved would have been more OSTs something which clings on to your mind, Sejeong and IU have done a wonderful job but I think it needed some more punch. Most of them were female sung I would have loved to see a male singer too.