I tried this a few weeks after it had aired because I saw how high the ratings were and here I am, finished watching this great mystery fantasy drama! I was hooked onto this drama since episode 1 and I was really intrigued by how this crime is taken place through parallel worlds. I stayed to see how this drama would and it sure did not disappoint! Another thing I loved is the moderate amount of romance that did not overshadow the suspense and crime-solving in the drama. Train shows how parallel world dramas should be done and I'm glad I stuck through until the end. Having 12 episodes was the perfect length for the plotline to develop at a moderate pace that was relatively easy to follow and did not drag. The only thing that made me drop a few points is that the story takes some thinking to keep track of each character's storyline in their original world because of Do won's world jumping. Despite this, it was a great watch and I would recommend it as a good suspense drama of 2020 to give it a try!

Spoilers ahead!
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Overall things I liked:
1. Very nicely written characters and storyline that was consistent and not boring (made it easy to get attached to the characters such as Kim Jin Woo's story, or the connectedness of the two worlds)
2. Love the acting! (Yoon Shi Yoon is amazing as the Do Wons!- really great as playing two roles which make up for his performance in Your Honor that I didn't really like; as well as the other characters)
3. The love line- was very balanced and did not get in the way of solving the mystery
4. How the motives behind people's actions were explained (such as why Min Joon killed or why the Chief protected him)
5. Filmography was great! (such as that scene in episode 11 when Do Won and Seo Kyung were both on the train tracks)
6. Loved how easy it was to tell when the world switched and which world each character was from without having an obvious personality or dress differences (I can tell based on behavior and can infer why that character turned out that way)
7. How handsome Yoon Shi Yoon was as Do Won!!- He got more built for the character and just wearing regular t-shirts look so good on him! >.<

Things that bothered me:
1. Some parts confused me at times because of all the thinking needed to keep track of the activity and background of each world's characters
2. How it didn't explain how Chief found out about the train or why Do won 1 had the power to move through the train at the end when the train was scraped
3. The ending!- I wish I could see more of what happened between that Do Won and that Seo Kyung in that new world shown at the end so it left me feeling unsatisfied