The series is basically about Ha Dong Soo, a man who has been deprived of a part of his body by organ hunters and becomes 'connected' with a person who has received an organ transplant. He soon realizes the man who has his stolen eye is a serial killer.

Well, it seems that people have mixed reviews on this series, and I am a bit in this case.
The summary of the series is a good sales speech, and I must say that I really liked the idea.

I'm a huge fan of thrillers, so this series is perfect for me in principle, and honestly I've found my interest to climb as the episodes go by. The overall story is very simple, and above all we can predict the relationships of certain characters a little, on those of Ha Dong Soo and Oh Jin Seop (the serial killer), or Ha Dong Soo and Choi I Rang. And in that sense, I still think it was interesting.

The problem with this series is that it is bland. Just like the main character, Ha Dong Soo. He spends his time suffering and just running and getting angry. He was basically acting like an angry, self-righteous kid who didn't know what to do with himself. And unfortunately, I expected more charisma, something from his character as someone who can regenerate and who is immortal.
In contrast, Choi I Rang, also a "Connect" had more flavor. I see some people didn't like her character for their own reasons, but I think her character was really good. She just had "it", this thing that makes a character interesting, she was mysterious, knew how to fight and protect herself, she knew how to protect her family, she is unpredictable and fearless. Exactly what I would have wanted for our male character.
As for Oh Jin Seop, the serial killer, I must say that his performance is not amazing, it is neither good nor bad, it is just in the same range as the serial killer interpretations that we have in general, same with his arc throughout the season. The aspect that I liked however is his M.O. That of making his victims a unique piece of art that is beautiful, it was really well done.

I must say that for the plot, it's essentially the characters running around, trying to meet and find each other. There isn't really insane element to expect. I liked the regeneration scenes of the "Connect" though.

However, it's the last episode that intrigues me the most. Obviously they hinted that this was all originally an experiment by scientists - let's act surprised - but obviously with this ending it's hinted that more might be uncovered if a season 2 happens. And for me, the most intriguing part is to see what will happen to Oh Jin Seop, is it possible to become a “Connect” ? A “Connect” which is a serial killer, well that would be damn interesting for the sequel especially to see the interactions between Oh Jin Seop and Ha Dong Soo.

I would summarize this series as an appetizer, and the teaser for a sequel would really be the main course.

So I do recommend this series overall, but it's not the not-to-miss type, it's good enough for a sci-fi thriller and promising for the future.