Like:
1.great actors and actress
2.story is good
3.undeniable physical chemistry of the main couple
4.good action drama
5.Lee Joon Gi is really good in action drama

DISLIKE:
hmmm... Nothing too much to dislike maybe the story is more great if the story it's not focus on revenge plot

IT'S BETTER IF:
1.the story is not too focus on REVENGE.
2.add some case to be solve
3.add some side story

Trivia:
This is the 4th kdrama(Two weeks, TBWD, Criminal minds) of lee joon gi I watched.