I'll say up front that you should give this show a try yourself and come to your own conclusions.

This was a really hard one for me to rate. My rating is based on the way this drama made me feel. I found myself unable to separate my feelings from the overall intent of the show, thus the low rating. As I feel I have to say so people don't attack me, this is just my personal feeling/opinion. This rating serves the purpose to remind myself what I liked and didn't like about the drama.

Story: Very interesting concept. I thought the way the story was woven together, with people's lives intertwined, was well done. As you go further into the story, we find Yi Jae inhabiting bodies of people that he's encountered before. We also see that his downward spiral was the result of his first encounter with someone's death. This drama embodied the concept of "every action has an equal and opposite reaction". I thought the story became more meaningful when it was personal, concerning his girlfriend and his mother. I just couldn't get past all the evil/darkness/bullying/violence. I probably would have enjoyed it more if time was taken to develop some of the characters more, to see why they became the way they did.

Acting: Can we just talk about the cast? I'll admit, that's what drew me to this drama. Each person was excellent in their own right, but the standouts for me were:
1)Kim Mi Kyung as Yi Jae's mother. I love this actress in everything she is in. Here, she embodied someone carrying the weight of the world on her shoulders after her son's death. Her slightly stooped posture, her slow, mincing gait, and her facial expressions (or lack thereof) showed us that she was walking through the world by herself, after losing the person most important to her. I felt her despair. Watching her face, her flat affect, a lone tear running down her cheek, it seemed that it was all she could do to just keep living.
2)Seo In Guk as Yi Jae. I'll admit that he's one of my favorite actors. Here, he hit all the emotions (even if there were only brief moments of happiness shown in flashbacks). Anger, fear, frustration. Watching him moving from hopeful to hopeless, wow.
3) Kim Ji Hoon as Park Tae Woo. Sociopath? Psychopath? His portrayal of an evil man masked as a successful businessman just gave me all kind of creepy vibes.

This was filmed in a very dark way. I understand that it was part of the whole experience, but some scenes were so dark, that if you watch it in a well-lit room, you won't be able to see what's going on. So, watch it in the dark.