I'm starting to think that IU is allergic to projects that have happy endings. That being said, this drama is unforgettable. The story keeps you engaged until the very end and the roller coaster of emotions will leave you bereft once you finish. The cast did a wonderful job, I don't think I can signal an actor that got a part that they didn't do perfectly. I highly recommend this drama.
My only miff is the ending and the fact that sometimes the story goes too much towards sadness. If you're hesitating on watching, don't. You will enjoy this gem.