I started this drama only for the sake of D.O. because I love his acting (and singing), and having read reviews I already expected that this would not be an amazing story. Of course there are cliches and tropes, and there were some things I found problematic regarding the plot and story, but I was surprised I didn't drop this midway and ended up actually liking a few things about it.

WHAT I LOVED:
A major plus point is naturally D.O.'s acting skills; his facial expressions, his voice, his gestures are all on point. He really became the character, and portrayed in the true spirit the amnesiac prince who is lousy and dumb at many things, tries to maintain an imperious carriage, but is kind-hearted on the inside. I also loved the costumes, the setting, the cinematography; it was all really well-done. The love-story itself is immensely adorable, and if you're going to watch this drama, watch it for the cute scenes between the main couple and for the sake of the masterpiece that is Do Kyungsoo. The humor is well-balanced, not too over the top, and well-placed. I found myself chuckling and smiling a goofy smile many times. The village life, the side-characters like Kim Soo Ji (crown princess's brother), Kkeut Nyeo and her husband, town officials, and others really brought the drama to life with their wholesomeness. I also felt bad for the crown princess, who was forced into a marriage she had no heart in, was the butt of her father's political intrigues and was essentially a prisoner in her own house.

WHAT I DIDN'T LOVE:
Major Plot-holes and weaknesses in story:
It really bothered me that Kim Cha Eon (Crown Prince's father-in-law) kept insisting that he had no son, yet we've got Kim Soo Ji wandering around claiming that he is Cha Eon's son. WHAT?? That's something no one can overlook. And you're telling me, Seok Hwan/Moo Yeon worked under the man who killed his father and threatens to kill his sister, for ten years, and didn't once try to find a way out of this deal?? And that he fell in love with this man's daughter, the crown princess, and even got her pregnant? And Kim Cha Eon didn't figure this out till much later?? I'm sorry but I just couldn't believe in absurdity like this. I also find it silly that both Moo Yeon and Yi Suh kept visiting the bridge on 15th of every month (okay maybe Moo Yeon didn't go there often) but they never once met up. Yi Yul had two sets of memories to retrieve, I found that bothersome. Jae Yoon rescued his eunuch after the latter's throat was slit, and didn't tell Yi Yul about it till much later. There are arrows flying everywhere, and too many flashbacks. Yi Suh seemed to have no purpose in life except to wait for her brother, and neither she nor her brother seemed to want to take revenge or at least seek some sort of justice. Yi Suh's adoptive father was really problematic; I found him really uncomfortable (heh). He should've realized that the man he was rescuing had a wound from an arrow, which would mean he was either a runaway convict or perhaps had been caught in some battle and it should've been a red flag. He also wanted to keep lying to Won Deuk/Yi Yul and Yi Suh. Jae Yoon's connection with the gisaeng was also weird. That was such a weird, unnecessary and random plot move that I don't even know what to say about it, except I wish they'd left it out.
Acting: This is the first drama I've watched with Nam Ji Hyun, and her acting left much to be desired. Her facial expressions are very limited, she didn't seem flustered when she should've, she often stared blankly back at Yi Yul when he would express his desire to stay with her or marry her. Compared to D.O's acting, she paled.
Characters: Most side-characters have little or no backstory and seem mere cardboard cutouts; I wanted to know more about Kim Soo Ji because he seemed like a very interesting guy. I also wanted at least once flashback to explain how the crown princess and Moo Yeon developed affection over the years. Theirs was such a strange love story that I felt nothing toward it. There was no chemistry and no backstory to prop it up. It felt so hollow I can't even begin to talk of it. That loan shark guy in the village was also very strange; is he a good guy or a bad guy? make up your mind.

In short, don't watch it for the story, just watch it for a light cute romance and for admiring D.O's acting.