Reading the synopsis, the description and looking at the picture had me thinking this was a Rom Com, something I could watch with very little angst. This show, to me was veering very close to melodrama. Don't get me wrong, there were a lot of really funny scenes, but I think I might have enjoyed it more had I been prepared for the heavy subject matter.
Acting:
Kim Myung Soo as Dan was good. He was excellent at the physical comedy aspects of his part, and can we just talk about his dimples? He got into trouble when trying to portray anger, then his acting seemed a little forced, and sometimes even watching his walk, he didn't seem comfortable.

Shin Hye Sun as Lee Yeon Seo is wonderful. I loved her in 30 but Seventeen and she plays a completely different character here. She's mean, short-tempered and unlikeable. For me, I was a few episodes in and I hated her (as I was meant to) and wondered if she would ever change. She played a ballerina, and she has the perfect, really slim body to portray a dancer.

Kim In Kwon as Angel Hu: I have to give a special shout out to him. He was exceptional. He was extremely funny when he was supposed to be, and was able to wring emotion out of me at other times.

Story: It got a little garbled in the last half. It seemed like another writer took over and didn't quite know what to do with the story. The bad guys were over-the-top. The multiple times of the main couple being together, apart, together, apart got tiring. I'll say again, why do most Asian shows short change us on the ending? You find out what is going to happen to the main couple in about the last two minutes of the show, and then it's over! I do have to say, the story of the old couple in the sanitorium was wonderful and it really made me cry. Some of the things didn't make any sense, like the second male lead - something happened in the second or third episode to show who he is, but then it turns out to be something completely different!

Chemistry: There was cute chemistry between the leads, but I never really "felt" them as a couple. I liked the fate aspect of it, but she was such a nightmare as an adult, what made him fall in love with her? It's a mystery to me. I have to say the comedic scenes were a joy to watch. And the scene toward the end with the leads and Angel Hu had me laughing out loud.

Soundtrack: Wonderful. The music was able to bring emotions to the front that I don't think the actors always had the ability to do on their own.

Rewatch value: There is so much out there to watch, and I didn't really find any scenes in this show that I need to go back to revisit, so the rewatch value for me is low.

One final critique: I have watched a TON of Asian shows over the past couple of years, and strangely, I always find myself fascinated with the jewelry the ladies wear. The jewelry is usually classy and interesting. In this show, they put Shin Hye Sun in the most AWFUL earrings I think I've ever seen. They were so bad, that a lot of times that all I could focus on. She is so beautiful and the earrings really detracted from that. Some of them looked like door knockers. Just very tacky, overall.

So, in general, I'm glad I watched it, but I can't say it was one of my absolute favorites.