I find this drama being a steady 8/10. Not perfect, but definitely not deserving the harsh negative reviews.

Bellow is my opinion regarding some points of the negative reviews:
1. Misleading poster: Somehow right, however only in the description of the Jae Yi character. She is actually far from devoted future wife and mother, being mischievous (in a good way) and with very modern understanding of the woman place in the society.
2. It is a mystery drama with none or very slow burn romance: Yes, I agree, romance is left more on our imagination than actual romantic scenes. While we would be happy to see more romantic scenes , we should take in consideration the story. Both lead characters cannot imagine having chance as a couple, hence the withdrawal from expressing their feelings. First, due to the historical setting, there are strict rules of who can be Crown Princess and our FL doesn’t answer the criteria. Second, the ML believes she belongs to another man.
3. Holes in the mystery story and poor writing: I disagree, all of the complaining reviewers are forgetting of the tombstone Jae Yi’s father found! That piece of stone is the connection. The other complain was for non developing the fantasy part - it had an explanation, just pay attention to final 3 episodes (not willing to spoil).

In fact all negative reviews dropped the drama in the middle, the unraveling is happening at the end :)

Acting is spot on!