The costumes, the storyline, the music, the scenery, THE PLOT TWISTS, THE WHOLE CAST GOD. Personally, I don't think I'll EVER watch a better Kdrama than this. This thing is a MASTERPIECE! The actors' acting is so freaking good, especially Kang Ha Neul's and Lee Joon Gi's! THERE IS TOO MUCH DRAMA AND I LOOOVE IT!! I would do literally anything to watch it for the first time again ( a piece of advise here, DO NOT spoil yourself, it's TOO PAINFUL) You'll shed rivers of tears, not only in the end, but in-between the episodes as well. I love this Kdrama TOO MUCH!! If you plan on watching it, have a great cry my darling!