I'm not gonna lie saying this: I decided to watch this drama because of the big amount of comments saying that it was a "No-No".
A lot of people dropping it and stuff like this.

So, I just got curious and decided to give it try.
Once finished it, I can tell that it wasn't THAT bad. I mean, I was expecting something definitely worse
(I prepared myself for the worst).
It wasn't a masterpiece but it was decent. I liked it.

The way writers built each character in a different way, with a different (and sad) background was really a good idea.
I liked that.
Still, I can understand why people lost their interest in it: there was no development. This is 'cause writers preserved it for a big finale. But I'm gonna talk about this later.
I think that another problem was Soo's character. He was so marginal, kinda meaningless. The writers weren't able to let viewers get attached to him. They could have worked so much on his character...
Talking again about the plot development.
The problem was this: the whole drama IS in the LAST episode, basically.
I'm serious. It was like the writers put all their ideas there. In fact ep. 16's finale was SO rushed. It's really a shame. This could have been a lot more interesting and entertaining and there could have been a different development of the story itself, but also of characters and their relationships.
A lot of WASTED POTENTIAL.
(OST awesome. I really liked it).