I didn't watch the 2019 Taiwanese version, so the review is based on my take on the Korean version alone.

The drama started out pretty strong. Jeon Yeo Been did a great job portraying two completely different personalities between Jun hee and Min ju. One was outgoing and popular, the other was a miserable introvert. The show also did a good job showing the chemistry between Jun-hee and the two boys and Si Heon's growing love for her. The high school timeline was the most interesting with the most chemistry between the three main characters. The adult timeline was kind of bland with Jun hee and Si Heon/Yeon jun having a much less dynamic relationship. This was the second drama I watched with Ahn Hyo Seop and he did a lot better here than in Lovers of the Red Sky.

While the show had a great start, the writers decided to make the plot more complicated than it should've been. By episode 9, I started losing track of who was who because the timelines kept switching and characters kept flip flopping between bodies. I wasn't sure what the connection between the timelines was either. I assume they were parallel universes with two versions of the same person living in both of them, I guess? But, then how did Si Heon and Yeon Jun meet at the airport if they were from different universes? The show also didn't quite explain the connection between them and how Yeon Jun even ended up falling for Jun hee. Maybe I missed it because I was trying to keep track of all the characters and timeline hopping.

Some plotlines got too extreme and others were kind of forgotten. In-kyu disappeared for several episodes, making his character kind of irrelevant, then appeared again towards the end trying to save Min-ju. The murder/suicide plotline was radically extreme. It would've been better if Min-ju just died in a car accident, instead of by some random obsessive classmate turned serial killer who traveled back in time in a body of his brother to train himself to be a serial killer. This is not to mention that the outcomes kept changing as the story progressed from all the timeline hopping, making it even more confusing.

I didn't quite get the significance of Rowoon's cameo as Tae Ha. Did it mean that Yeon jun was gay and was just starting to confess his feelings for his friend before the accident, and that Jun hee really fell in love with Si Heon and not Yeon jun? The writers spent no effort trying to flesh this nuisance out. And, did Tae Ha die in the accident?

The ending was very sweet and left a lot of questions unanswered. The only couple that made sense was Min ju and In kyu because there was no confusion about who was who. With ML and FL, I am not sure whether Jun hee ended up with Si Heon or Yeon jun. They acted like the same person. I think she met Si Heon at the end because Yeon jun was the one who got into the car accident, became a cripple, and got stabbed to death. Not to mention, he might have been gay.

Overall, the show left me with a lot of unanswered questions and some confusion about Jun hee/Si Heon/Yeon jun romance. On one hand, I liked their love story. It was very touching and bittersweet. On the other, all the timeline and body hopping made me completely lost about who was who.