I'll keep it short since there are already many other very thorough reviews, but this really is a lovely show for true romance fans. To start on a very superficial note: the leads are beautiful, the secondary characters as well. The costumes are wonderful, it is very well shot, and with its sweet, dreamy and melancholic atmosphere, this show is a real treat. The acting is strong, though perhaps Park Bo Gum shines even more than Kim Yoo Jung (whose looks are so ethereal in this show, she almost looked like an alien, albeit a very very pretty alien), as he conveys the giddy romantic feelings of his character (those cheeky smiles!)  as well as the depths of his sadness (those teary eyes!) wonderfully. His character is extremely touching in that he is very open about his feelings, all while being admirably witty and quick on the political front. This is a show that really treats its viewers more than the usual in the romance department (I would say about 10 episodes are purely romantic), though it does take a bit of a backseat in the last 2-3 episodes. However by then the drama had set so much intensity between the leads that I didn't resent it too much. The two secondary characters, aristocratic Yoon Sung and rebel Byung Yeon, are really worth mentioning as well, as their complicated loyalties make a very touching story. I loved how the drama showed examples of people intertwined in difficult circumstances that sometimes de facto opposed them to the ones they cared about, but how somehow despite their allegiances and actions they never betrayed each other at heart, because they were coherent with themselves and with their values, and because there was a general trust and respect amongst these characters that admirably avoided many of the cheap misunderstandings dramas often give us. Overall this show went above my expectations in terms of romance (compared to the regular romantic drama), all while maintaining a clever, subtle tone that never made me feel dumb as a viewer. It's a romance drama with quality.

P.S: I actually dropped this show several times in the first couple of episodes because it was perhaps a bit too goofy for me, though I really started to feel invested around episode 3 when the leads start to connect more.