I started this drama for many reasons.
It became extremely popular in Korea, the viewership is already so high ( even if the drama is still airing ), it is 4th most viewed TVN's drama after Goblin, Reply 1988 and Mr. Sunshine. It has the North Korea topic, which probably also drew attention of korean and foreign viewers. The main cast is well known and loved, I think we can even say that they're legends. If you liked "Beautiful" by Crush, you can also enjoy his new ost made for this drama. Sounds like a full pack, an ideal drama, right?
And well, in my opinion, it is.
I've watched many great series, and I'm sure - so do you.
But honestly, this is a masterpiece. The way in which actors and whole story catch your attention and engages emotions is on another level. First episode may look a little bit cringey and unnatural, especially when it comes to See Ri's behaviour, but please don't be put off by it. Just watch it till the 2nd ep and you won't even notice when you'll be totally into the story.
And my advice is - don't watch it too fast. Just enjoy every episode. One, by one.
I watched only 6 episodes so far, but I already know this drama will end way too fast. Every episode duration is about 1 h 20 min, but really, I feel like it'd last only 40 min or even less.
This story is just different. There is no other drama like this.
I promise, you'll be surprised.
And you'll be even surprised how the writers used typical cliche for making it even more entertaining.
You just won't expect it.

Anyway, I'll update this review after watching whole show.
It's my first review, and my english isn't perfect so please bear with me.