Acting was great, yeah it was violent and gratuitous but action was well done at least.
WARNING: There is lots of blood, violence, and some sexual violence or an attempt at it. Definitely not family-friendly LOL.
I got engaged even though it was very predictable. Called twists in Ep 1 and yet still was crying when they happened. Han So Hee is such a great actor and Ahn Bo Hyun is so charismatic... I knew it was over, like really over and still wanted more, which is abnormal for me with shows! Wow!
Han steals the show with amazing body language, understated but powerful dialogue, control over minute facial reactions that convey so much, (one scene in particular with Ahn Bo Hyun I still remember her slight smile... wow) and you come back each episode to see how what's next for her and her journey. The other characters around her and storylines don't steal the show but compliment the main plot well. It's part bloody revenge plot, part spy drama... ooh I wish there were more!
EDIT: Other than predictability, music wasn't super memorable for me but so much was enjoyable that I kinda forgot about it and it didn't detract from the experience.