Unpopular opinion, but I couldn't get into this drama. I thought it was mediocre at best. Maybe it's because I'm generally not into fantasy, which (obviously) this is. But even aside from the fantasy elements, there was something about it that kept me from caring about the characters and feeling anything for them. I didn't feel truly drawn into the story and I couldn't quite pinpoint why.
A big part of it might have been the FL. I'm not a fan, she always does the same dead fish look with a blank expression and her mouth hanging open in almost every scene. Her character here has good backstory and she showed a bit more acting skill for sure, but the personality she had her character portray was godawful. Cold, flat, boring, almost masculine and I didn't feel any chemistry from her when it came to her interactions with the ML. I dropped it at episode 7.
I thought the ML was a different story; he was the one character who kept me watching. He's a good actor and his character actually had dimension and personality. But the romance was very elusive and a mess. He likes her, but does she like him, or the crown prince, or her childhood sweetheart....? Does she even have feelings for anyone at all, since she never shows any emotion?? Idk the whole drama was enough to keep me kind of interested and keep hoping it got better, but overall bored me. I kept having to fast forward long palace conversations. Something would occasionally happen to make the plot seem like it was going somewhere exciting, but then they'd cut to scenes of one of other several side characters and the little exciting twist wouldn't amount to much.

If you're in the target age group for kdrama fantasy and enjoy the genre though, you'll probably like it.