This show has a lot to offer and you will probably find something that pleases you- I'm not a big fan of fantasy or action shows, but these themes was worked very tastefully, having also time for the romance and mystery portions of the plot to flourish. The visuals are outstanding and really set a new mark for korean dramas, the overall plot keeps you guessing and looking for the next episode, leaving and ending on a strong moment to lead to the next season (also it didn't leave the first season weak or unresolved to the point of it lessening the enjoyment).
With that said, I found the romance and characters to be a bit annoying, especially in terms of romance. There's almost no chemistry between the two main leads, even if the spend a lot of time together. FL shows more affection to literally any other male character than the ML. There's the classic love triangle, for both the ML and FL but when the FL is constantly showing way more affection and reason to believe she likes the second love interest, to this the ML appears sometimes sad but doesn't act jealous or anything, and the ML's love triangle is almost non existent. It's not enough of a reason to drop the show or ruin it, but I find myself annoyed with their relationship.
The music is pretty good too, I wouldn't say it's enough of a reason to watch( there's other dramas with way more unique or interesting music) but I never felt like it wasn't the right music for the scene.
The acting is amazing obviously when you have some of the most recognizable actors and actresses here. Tho, I don't thing the show has a lot of jaw dropping scenes where you feel emotional with the acting, it just very consistent and believable. Also the FL is very fun to watch, probably one of her best roles yet.