The Unquenchable Mr. Kim sounds stupid and corny, I prefer K's Secret.
Story: "Employee Kim Doyoon has been working for 5 years. He has one secret that he can't tell anyone else - the fact that he's a half-vampire born between a human and a vampire. One day, a single mistake turns his whole life upside down." Just from that explanation you can kind of get the gist of it. Sorry about it being so vague. I do like vampire stories, but this one, not so much. It's ok.
Art: It's decent (which isn't that good). The art looks weird in the beginning but I got accustomed to it. Like the facial expressions are unappealing. The H scenes are mediocre.
Characters: Kim Doyoon, the main character/uke, reminds me of Go Siwon from A Guy Like You. In a bad way. He is just too dense towards the seme's feelings. Then we have the seme, whose name I forgot so I'll just call him Director. Director is forceful and doesn't really take Doyoon's feelings into account at all.
Overall: 3/5 stars
A decent manga, I'm still reading it. It's bearable.