Had low expectations for this drama but was pleasantly surprised. It's my first time watching Seo Kang Joon and I was very impressed by his performance. Acting out duel roles can be very tricky and hard to execute properly, and I thought he did an excellent job to the point where I could have mistaken him for 2 separate actors. He nearly impressed me as much as Yeo Jin-Goo in The Crowned Clown (although that show still takes the cake for Top 5). I was hoping the sci-fi factor would veer a litttttle bit into fantasy by somehow giving him true chemical emotions and sensation near the end. I was craving a good cry out of Nam-Shin III or a reaction out of pain, but the emotional depth he was able to show near the end was very satisfying. I really liked the FL and Young Hoon. Their chemistry with both Shins was palpable (in platonic, romantic, and angry scenes).
It was interesting to see how the dynamic between both Shins and the FL and Young Hoon changed throughout the show.

Overall, I don't know if I'd watch this show again, but I think it's worth the watch nonetheless.