The end of the show makes you disappointed , sad , cheated and complexly frustrated.
They just made the fool of the audience who invested time , money and most importantly their feelings with the show.
This show is a revenge story with a super amazing plots and twists and keeps you on the hook for 15 episodes, the excitement reaches to sky level on hoping how amazing the ending will be but the writers disappoint you so terribly that you just want to bang your head.
The show would be enough if you watch episode 1 and episode 16, the 14 episodes in between are total waste, have no significance what so ever in the journey .After watching the final episode you keep asking what is even the meaning of showing the awesome bonding between grand father and grand son. The ending totally killed and disqualified the whole process.
so many questions and so many leftovers , either the writer go lazy or it is the classic case of starting/thinking this amazing/intriguing plot but not knowing what to do or how to deal with it. The writers got buried under their own weight by not able to figure out answer of the question they created.

Yes, song jong ki is amazing , he always is , the guy playing grand father is excellent and all the other characters were also good , music nothing to talk about ,the love story was never in the forefront but the bland acting of female lead made it non existent .

final verdict - Watch only if you are fan of SJK.