I'm not an exo fan (please don't kill me xD) so it was a little more difficult to watch, because I didn't have the fangirl motivation here xD
Someone said is a shopping king Louis in joseon and...well that's where the problem lies. Everything, like every trope of this drama it's already seen and already done. The similarities with skl are many, but also with like every period drama I have seen. (Speaking of which: there is a saeguk not focused on the royal family? Or at least not only, like there's nothing else to write about that period??) There's no suspance, no really twists in the story or mysteries - we all knew that the assassin brother was the father of the queen's baby. Even the death of the evil vice minister was unsatisfying...well the whole plotting against the crown was too bland and boring.
Also! There was the "solution agency" which was an interesting thing, but they drop it pretty soon only to bring it back at the end just to feign ignorance about the fact they forgot about it lol

Ps. My extremely unpopular opinion: I had the second lead syndrome... I felt much more chemistry between Hong Shim and the magistrate...maybe because I liked more his characterization or to me he has better acting skills (not saying the ml sucked...I just preferred the sm) when he almost proposed at the end I hoped they would've take the "realism" route and have the prince marry a noblewoman (ugh bitter isn't it?) and let them become a couple.