( I don't consider what I'm writing as spoilers since I'm not spoiling anything, but to some it may be so that's why there's a warning.)

Story's Message-
I think perhaps someone else noticed this before and may have written it in their reviews ( I haven't read anyone else's). When I was watching this drama, I felt there was a message being delivered and it seemed very clear to me. The robot (NS III) represents what humanity fails to do. If you take the supernatural abilities away from the robot, and look at the personality it has, it represents what you would consider an actual decent, perfect human being. The robot is shown to be selfless and even if it has suffered because of terrible humans, it still did not stop to help other humans. At one point when he was traumatized because of what a human has done to him, he was reluctant to help all humans but went back on track and helped humans when they needed to. He followed what his rules were. As humans we still harm one another yet this robot does not and this robot helps humans selflessly, while majority of us humans cannot do that. Throughout this drama, you see most type of humans.
-Humans blinded by monetary greed.
-Humans blinded by love/loyalty and are willing to do anything for that person.
-Humans with deep wounds that take their anger out on people. (Humans seeking revenge as well)
-Humans wanting attention and doing anything to receive the attention they want.
The list could go on. But around them, there is this robot who is clear minded. The robot has people precious to him as well, but doesn't lose sight of who he is. NS III doesn't take revenge or his anger out on the human race for tormenting him. You could argue it's because he cannot feel anything, but as his development continues it feels like he does have some sort of feeling. I think the story's message was something along the lines "that no matter what you're going through, don't lose sight of what you are- a human being; and to come back to being a human being."
I also feel as if there's also another message in the drama. When someone stands out in society or is different than the majority, we tend to pick on that person and make them miserable. In this case it's a robot. But you can replace this robot with someone else from our real world. Cases where someone decided to break tradition or something normal and was hated or mocked at for being different (excluding psychopaths & sociopaths).

Characters & Acting& Drama Overall-
When I was going into this drama expecting there to be romance between a robot (NS III) and a human, I will admit I was a bit weirded out. I wasn't sure how it would play out since I never watched a drama where a robot and human are a couple. I have to say this drama wasn't so bad with its romance between a human and robot. I actually didn't mind it so much, I found it very funny and adorable at the same time. That being said, I did wonder about some technicalities-- the physical and emotional aspects of the relationship which they didn't show much because it may have been complicated. A robot cannot feel anything which was mentioned several times (and it's common sense) but at the same time you see NS III's development as if he were a human being. The show's characters also have this confusion that we viewers have: "He is a machine, but acts as if he were human and develops as if he were real". How deep does that development go in a relationship? We slowly see through NS III's actions that he cares for the person who loves him, but he cannot verbally communicate about his feelings until near the end where he did. I just wonder if that development for a robot would go to the point to have a sex drive? I have seen cases in reality where some people have these dolls that look like human beings and some of these people do claim to have sex with them so I know it's possible to somehow have sex between a robot and human. They didn't want to explore this in the drama so I'm fine with that. I was just curious because it's a robot that is like a human instead of a doll and if it would develop to that point. But, the drama's main focus wasn't that so I let that thought slide and not let it affect my view on this drama.
I think this drama did a great job of developing each character whether it is the protagonists, antagonists, and people in the middle/side. I'm glad that the story decided to develop the human NS character as well because most stories with a good twin/evil twin tag don't really focus on developing both the characters. It usually focuses on one of them. And this story may have focused on the robot NS a lot, but it didn't leave the human NS character empty. The one thing I will say is that I did not like how they progressed the human NS character. I'll leave a comment in this review with a spoiler tag to go in depth with the characters. I do feel the drama was a bit rushed and some things could have been cut out to make a better ending.
The acting was also wonderful. I don't think anyone in the drama overacted. SKJ did a wonderful job of portraying two distinct characters. I was honestly shocked because this is my first drama with him and had lower expectations.