This was one complicated drama. It is the only drama that got my brain working too hard till I gave up theorizing.
But the ending and another ending on the special episode shine some lights into the questions I had for the last eps.

First, a standing ovation for the production crew and director. The actors said that the director was very precise on how the story will go on and how they act their characters (kudos to that).

Story wise: It was long , complicated and detailed. But after watching the interviews with the actors and the last extended ending, I get why they had to make it long and detailed. The story line was made so that viewers will be able to understand the whole story (it was told in many different perspectives).

All the main characters deserved standing ovation too.
Lee Seung Gi (Jeong Ba Reum) is really breaking barriers with his acting career. Him playing a serial killer is truly amazing.. the way he portrayed the serial killer sent shivers down my spine. Originally I though he will be the good guy but boy I was so wrong. He fooled viewers really well hiding behind the "good"character. His gazed and eyes when he was revealed to be the serial killer is truly scary.

Kwon Hwa Woon (Sung Yo Han) character was too mysterious and had everyone thinking he was the serial killer. But as we were revealed the truth later on, I took pity on him. He was one of the most pitiful character in the whole drama (the other one is Det. Sang played by P.O. who got wrongly killed off later towards the end). His acting was really good portraying a cold character.

Lee Hee Joon (Ko Moo Chi) scene when he witnessed his brother getting killed was truly heartbreaking. He deserved an award for that scene alone. I'm gonna miss his rough but soft heart character the most. He really is a good actor.

As for the girls... they portrayed their characters well. I sympathized with Bong Yi a alot and I think she forgave Bareum in the end as he was her first love after all.

Overall.. this is one drama that got my brain so tangled up in the theory of who is the real killer.
If you can stomach serial murders story then please watch this. True, all murders are cruelly described but was blurred completely so it won't be too visuals for people to see.
Although I won't watch it again anytime soon.
Hope other people will enjoy this drama as much as I did. ^^

PS: The OST hv some really good song. Check that out as well.