I personally enjoyed the drama I just wished they gave more depth to Rin. I wish we go to know more about her past to understand her relationship.
Rin boyfriend also deserved more depth. They did not explain what was in the letter which was annoying.
The main leads relationship was very refreshing. We really got to see in my opinion at least a healthy way to deal with an ex. Though it took them forever the did communicate their feelings and were able to resolve and rekindle their relationship.
Sun young on the other hand didn’t have any character development which I wish she did because her relationship with Gun would’ve been so much better.

Overall show was very realistic, people are flawed and people don’t communicate in relationships properly and we get to see that.