While watching this drama I felt that the love story isn't that important and that the drama strifes to tell a lot which isn't possible in the given amount of episodes. Like a proper love story for example or more background about some of the characters. Regarding the antagonist's goals I wondered why he invested so much time into useless stuff. First it felt like he wanted to become the king, which was impossible anyway - but why all the chaos just to get a flute? I guess that could've been solved sooner.

Further the storytelling tended to be confusing from time to time regarding all the time jumps. Not actual time jumps, but what happened in a previous episodes sometimes only continues at the end of the next episode, so I tended to wonder "what time is it now?". Time was a huge factor in the whole drama and I think it's one of the reasons why the love story seems to be "rushed". I guess the time that actually passed was different from what we watched, so certainly I tended to ask myself as well "Why do you love him now?" or "Why the heck are you crying if you'll just meet again?". Similar in regard of Mrs. Koo who for some unknown reason killed her doppelganger. Seriously. What for? Lots of decisions seems to be just ruthless without putting much thought into them.
Still I liked the structure, I liked the efforts to put some science into it, I liked the music (which isn't always the case, I dislike most korean drama "songs" since they all tend to sound the same) and some of the twists.

On the other hand they showed the darker side as well in my opinion. Just like when the fl is kidnapped and goes on some sort of killing spree or when Lee Gon just slaughters everyone and turns his continuous joke about beheading someone into reality. There were funny moments though and after Mad Dog it was nice to see Woo Do-Hwan again.

I certainly don't regret watching this, but I just felt there could've been more to tell, more reasons to develop (the antagonist kinda reminds me of the guy from "My Love from the stars" - he seemed to have no good reason for anything either, I prefer something more reasonable). I feel like I watched some fairytale now - an entertaining fairytale certainly.

Some mentioned the product placement and I noticed it as well. I mean, I'm used to all Koreans eating at Subway by now, driving Kia and all Chinese using Apple phones. It's just like that. Here it felt indeed a bit ridiculous to hear real advertisement phrases from the characters. So I agree, they overdid it.