LIKES:
Lee Joon's acting in this crime drama is superb. He became a psychopath and even gave me chills a few times. I liked Tae-oh and Jiwool's moments together. She was naive and compassionated with Tae-oh, but utterly stupid around Mad monk. When the drama focused on Lee Joon's character, especially in the beginning episodes, it was really good. I like that the show focused on murderer's psyche and not so much on the victims. The music was okay too and the FXs were decent. The cast was well selected for their roles. I liked seeing Jiwool's webtoon.

DISLIKES:
The writer failed on so many levels; plot holes, unbelievable moments, etc. [See end of review for Spoiler of one of the biggest writing fails.] Production was good in some parts, but total crap in other ways. They had a bad case of shaky camera syndrome going on in each episode. Sometimes it was so bad it gave me a headache. Mad Monk got to be very annoying , but out of all the police seemed to be the least stupid, but towards the end of the drama his storyline became idiotic [See end of review for Spoiler]. Throughout the drama the police were made out to be morons. Maria, aka Dr. Oh was another moron and there were a lot of conflict of interest moments, that the writers failed so bad. She also contradicts herself and makes her profession seem ridiculous. Some parts the story gets boring and they repeat scenes over and over, which is unnecessary and lengthened the number of episodes. The plot twist wasn't too surprising, but was okay for a "who done it" drama. The ending was very rushed and seemed to be slapped together, it was disappointing how they "resolved" the crime drama.

OVERALL: Watch this for Lee Joon's acting!!! This is his best drama ever. I liked Tae-oh and Jiwool's interactions the most, so much so I wrote an alternate ending fan fiction (Gap Dong: Chosen By The Beast). I do recommend watching this and I did rewatch it (and bought the DVD).



SPOILERS:
Moo-yeom's brain injury portion of the show was stupid, didn't add to the story and seemed an easy way out for the writers.
In the scene were we see Tae-oh as a child, where Moo-yeom tells him that the person who killed Tae-oh's father was Gap Dong. The writer failed, because the murder scene is still being investigated by police, the body is there with all the blood and yet, no officer stops the kid from entering the area, contaminating the scene (his foot touches the blood) and seeing the body. Ridiculous! Maria Oh as a psychiatrist is stupid because she's still traumatized by having been a victim of Gap Dong the original. Same reason why she sucks as a profiler. Ji-wool is the perfect person to show how manipulative psychopaths can be, especially Tae-oh .