I liked :
the ML, Jo Jung Suk is great in this show, probably his best performance !
The story is fine
The supporting characters are good, the villains are bad (very good actors), I enjoyed the queen dowager (actress was so good in the crowned clown) , the first king Choi Dae Hoon, Yang Kyung Won (who was also good in Vincenzo and Crash landing on you)

I dislike :
The Female Lead ! The actress is so bad ! She was bad in rookie historian, she didn't change !
Someone can tell her that to keep your mouth open during all the series is NOT an acting skill !
She spent less than 5 minutes with a closed mouth ! She has no facial expression, she just rolls her eyes lol
Zero chemistry with the ML, always the same face.
The character is not better, at the end why did she leave ???
It s a bit long, especially the last 3 episodes.