I don't usually enjoy school dramas and time travel concept but in this drama, their present adult life and their past school life are going on in a parallel. They switch the scenes so smoothly and you'll get the balance between the fluff of youth love and also the maturity and angst of their adult life in every episode.

While watching, I'm in awe with the writer's mind. You can tell they did their research or they get inspired from traveling or reading materials, especially when the main leads are in Venice, whenever they started talking about books, art gallery, movies. You can't make them up without personal experience and deep research. Kudos to the writer for that.

All the actors play their characters so well. Their personality and visuals fit their roles whether they're playing as an 18 y/o or 30 y/o.

Now to the flaws, there are too many episodes. I don't find the story draggy but they're repetitive. There are many parts where you'd think "this is perfect as the ending", but there's still so many episodes to go so they created more crisis. It went on several times. This would be a perfect drama if it only has 16 episodes.

Another thing that bothers me, with all the time travelling confusion, the side characters sometimes disappeared for several episodes without explanation. It doesn't really affect the story but I keep thinking in the back of my mind where did her parents, his grandpa, his assistant or even their dog go to?

Overall, this is a really good well thought out drama. One of the best modern cdrama I ever watched.