Definitely one of the better vampire stories I've read. It feels very 'grounded', with the vampire angle serving mostly as an adjunct to a Korean court intrigue story, and both angles of the story reinforce the other and feel like they fit naturally together.
The idea of (midway spoilers for the main intrigue of the plot)
a vampire who's been living in the shadows since the founding of the current dynasty, and has been doing their dirty work in secret
is fascinating and well-executed, particularly with some of the later character development (ch ~50ish spoilers)
when he decides that he's seen enough of the evil side of maintaining a kingdom and it's time to just kill them all and be done with it
.
The ambience is mysterious, although it never feels like it's just stringing you along by baiting reveals, and the characters are likeable and grow on you, or they're at least funny.
I do have one complaint about the first part of the final arc, in the category of characters making incredibly dumb decisions to generate more drama:
when the Catholic/Chinese vampire hunters turned vampires show up to kill the secret vampire in the palace, they decide to go take their personal revenge first, which ends up decimating every character who has a chance at helping kill their real target. That was dumb. That was REALLY dumb. And they hadn't been necessarily set up as impulsive hotheads before that, so it was kind of out of left field.