I'll start with the actors — The actors did a really great job portraying their characters. It's like it was made especially for them to act. From the female lead crying and acting tough and the male lead acting like an idol, swimmer, etc.., to the antagonists annoying the hell out of me. Bonus point to that is the chemistry of everyone.

For the plot — I have seen other K-Drama with the same "time-traveling" plot, but this one added some twist & turns on it. It kept me on edge until the end. Usually, when I watch K-Drama, I skip 1/4 of its scenes as there are of course awkward and cringey scenes but this one, if you're into sweet, kind-of childish couple, you would find yourself watching almost every part of it without skipping.

Finally, for the storyline — Of course, this isn't a perfect one. You would still find holes in the story such as "why is the grandma like this" or "why is the watch the "portal"" but I guess that might get answered by the Season 2.

Overall, it's not a new concept of K-Drama, but it does deserve the hype.