It's crazy. I watched a lot of kdramas before but this one hits differently. You know when you get a perfect combination of cast, chemistry, superb acting(Seo In Guk's acting is impeccable and Park Bo Young's acting is so natural ), great cinematography (kudos to the director, every scene is so beautiful and pleasing to the eyes), great OST, great script, great directing(i watched the BTS and saw how detailed the director was with each scene and dialogue) , great side characters .
Sure, there must be some flaws somewhere (which don't really affect the experience), as no drama is perfect. but this is soo soo worth it to watch. The sad scene isn't forced, the message that it conveys also was delivered very naturally without forcing the idea into your mind. Once watching it, you'll realise that, oh, how beautiful life is , because it's short , because we die. Myeolmang is portrayed as a character that never dies but such life is so lonely.
I never repeated a drama after it ends, but this one, i watched for the 7th times already. Try it.