Hi. It is the first review I have ever written, but this drama was so hard to judge, that I want to share my own point of view on it.

First of all, it is not an avarage revange drama we all used to. In my opinion it definitely is not a makjang, rather a solid thriller. Some twists are unexpected and, yeah, even genius. Some shots are brilliant and daring, much better than in nowadays dramas which are beautiful but in the same time mostly conservative.
Romance is balanced. In one of the last episodes I witnesed one of the most touching kisses I have ever seen in drama (you can check my watchlist, I really have seen many of them).
Of course Kim Nam Gil is brilliant, but others actors also do the good job (among them we can find young Lee Soo Hyuk).

So, a riddle is: why so good drama does not have a better rating?
Watching this drama is like bilding house of cards when with last card everything is ruined. So the bigest problem, in my opinion, is the ending. It is so rushed that viewers are suprised by it and do not really have a chance to relate to it emotially.
Also some parts of the drama are exaggerated - but it is an issue with dramas in general, so I don't really consider it as a flaw - and female lead's acting is not always on point.

To sum up: I recommend this drama to all people who love quick, gripping and in the same time touching stories with deep characters. But you should be aware, that some threads will not be developed as you wish and in the end you might be disappointed. It is a entertainment that comes with some risk.