This drama is a must watch.
The first few episodes may come of as confusing, but once you're past that this drama will take you in for a ride. And it's an amazing ride.
The casting is perfect, the female characters are complex, smart and strong (every single one of them). The second male lead is another perfect character with so much to tell. Overall all the actors have done their characters perfectly.
The villain is great too.

Personally this is a perfect drama with time travel, adventure, thriller, a crazy villain, best female and male characters, romance, heart wrenching drama, having perfect dialogues and ending.