I really recommend watching this series for many reasons:

All the actors and actresses are great and they fit the characters so well. They all made me cheer, cry, hate and love them.
Even if the main lead, Saeroyi, was annoying at times, the actor, Park Seo-Joon, is amazing in the role. My favorite character, one of the main female lead; Jo Yi-So, who is played by Kim Da-Mi is a perfect fit too.

The music is one of the best in any kdrama I've ever watched, so many good ones, and it worked with the story as well and never felt like an odd choice.

When it comes to the story, I loved to watch the story of how cruel life can be, and how we never should give up fighting for what we believe. I love how our main character learns what's important in life. The only thing that makes me not give the story a higher score is because of all the love triangles I realized I didn't really care about. It made me annoyed many times how characters kept loving people that clearly wasn't good for them. When watching, I felt like a lot of the love didn't make sense. Why does she/he loves this person? It felt like they just loved for the sake of it, to cause drama. But other than that, this series is a roller coaster, and I loved every episode.