The Time travelling theory itself and how it was portrayed is muuuch better that other kdramas with similar genre (im looking at you The King: Eternal Monarch), you kinda have to rewatch it to understand it better on how it works if you dont get it the 1st time.

The way characters portray while moving back and forth during the different timelines its more visible and easy to understand, something that other dramas tend to fail to address properly.

It does have flaws tho, for example there where some scenes where the music didnt really fit the vibe it was giving.
But other than that if your into Time travelling kdramas, you should go blind and skip reviews, its better that way to enjoy it.