I want to share an article written by Lee Woong of Yonhap News at the end of the drama. It was translated by my sister, ChoHyeri, who used some parts for Wikipedia; the summarization of the last two episodes wasn't translated (it's marked as [...]).
"The tragedy of love"... 'Moon Lovers' ending with a viewership rating of 11.3%
Perhaps all love is tragic. It is not because of misunderstanding, jealousy, or selfishness. It's because one day, the ideals it's chasing have to be broken in the face of reality.
SBS drama 'Moon Lovers' faithfully portrays the tragedy of this love. It has produced an irresistible catharsis by compellingly polarizing the tragic contradictions that love actually has.
According to Nielsen Korea, a ratings research company, on Thursday, 'Moon Lovers' closed at 11.3%, the highest nationwide rating. The average viewers rating of the 20 episodes was 7.6%, less than expected. However, it produced a number of fixed fans and showed high popularity that far exceeded audience ratings throughout broadcasting.
Its response from overseas was also good, with the cumulative number of views surpassing 2.1 billions on the Chinese video platform Youku.
[Fantasy showing the tragedy of reality]
Based on a Chinese novel, 'Moon Lovers' is a fantasy historical drama about a modern woman who time-slips and falls in love with the sons of the king. However, it didn't escape or glorify the tragic reality as any other fantasy did, but rather used the fantasy as a dramatic device to show the tragedy of reality. [...] 'Moon Lovers' portrays a love that withered in the face of power. Fourth prince Wang So and eighth prince Wang Wook, who fell in love with Hae Su, bet everything for love. And they compete for the throne in order to gain love or because of the loss of love. But in the end, everyone loses love in pursuit of power. The Goryeo Dynasty visited by Go Ha-jin was a stage for dramatically exposing the same contradictions we experience in the ordinary life. [...] 'Moon Lovers' portrays the contradictions of life that inevitably lead to an end.