This drama used Korea's leading script writer. The production values are at cinema movie standard throughout. The monetary cost of some of the scenes is way beyond almost all other dramas. The plot is tangled and can be taken at different levels. Mathematics is a theme and Einstein's theories are referred to in the set up of the story and this is a clue to understanding the plot. Better educated audience members will appreciate this drama more fully than those who are not. But it doesn't matter, because the show has a strong fun element, frequently poking fun at itself, so if like me you are not strong on Einsteinian spacetime math, it is still enjoyable and you can get the gist. However, this is hardly your average k-drama TV. That is why it did less well when it aired than expected. It is too high order for the average TV audience.
The casting is perfect. Lee Min Ho's screen presence in every shot for the whole series is strong. The director used Minho's beautiful smooth deep voice like a sound track throughout. His voice becomes almost mesmerizing as it is seldom out of one's ears for long. This is a unique and unprecedented feature in a k-drama and it is a strong point giving a fairly subliminal aural continuity throughout the episodes. It was very soothing too. This drama is a truimphant showcase of Minho's acting talent and it is impossible to imagine any other Korean actor able to perform so naturally and commandingly and with that voice.
Goeun has a very difficult job. First she is Minho's love interest when as i have just said his brilliance is shining and any co-star is likely to look second-rate or worse against him. Goeun also has to play a tough cop at the same time as a girl Minho, a King, would fall for, plus she has to play a part in 2 timezones and a double of herself in both timezones. Most Korean actresses couldn't get near acting this part. She gets better with each episode. She deserves an award for her achievement. She is the emotional epicentre of the series and her diverse part compliments and off-sets Minho's needing to stay magisterial all the way through. Although, hilariously, Goeun knocks him of his perch quite a few times!
This is the most postmodern hybridized drama ever made. It is a historical, political, romance, melodrama, comedy, farce, action, pychological drama all at mixed up, sometimes doing two or even three genres simultaneously. For an audience that can see and appreciate this it is easily the best k-drama ever made. But also, the intelligence of the drama was its weakness and why it wasn't able to retain a wide audience despite the large sums spent on the hype and marketing before and after it started airing, and why it's not a drama that the average viewer is going to like, because its going to be over their head.