It was one of the most heavy budget drama with a unique story and characterization but yeah it failed to impress the audience.
Kim Gu eun and Lee min ho Chemistry was so off that the entertainment agencies has to spread rumors, that the both stars are dating. This base less rumor also didnt help in increasing the TRPs of this drama .This show was rejected by the audience in Korea but on international platforms it some how did well.
The King eternal monarch story started with the parallel universe concept which was a new thing to watch but in the middle of the series it started loosing the grip on story. They added time travel element but just couldnt justify the senerio of the brutal killing of the King.As the male lead travelled multiple times in past but just couldnt make it to the right time to save his own dad.