This show was about halfway there to a really good show, hence my rating.
First what was good: the concept/story was interesting and original. Some of the CGI was decent, like wounds healing and the cool blurry-super fast running. Most of the time the acting was really good.
Lee Yoo-Bi as the adorable Jo Yang-Sun was a lovely breath of fresh air, a female lead who was ridiculously cute and pretty and just so easy to like - I felt like I was falling in love with her myself, so I could see why Kim Sung Yul did too. She was also a very good actress!
Lee Joon-Gi is great in everything he does, and he really gave it his all in this, but there were certain scenes that just felt super cringy, although I feel like that was more the fault of the directing and writing than his acting.
The star for me was actually Lee Soo-Yuk as the evil vampire Gwi - he was INCREDIBLE and honestly stole the whole show. His character was enigmatic, ruthless, sexy, and cunning, coupled with an incredible look (the hair+wardrobe+makeup was stunning!) combined to create the most interesting character in the show. I actually would have loved to have seen a flashback episode of his character.
Now for the bad: there were a LOT of silly/cheesy scenes in this. The angst was almost too much for even me, and I love me some angst. Also most of the music was terrible - there were a few background music pieces that were good, but most of the time a serious and well acted scene would feel overacted and over-dramatic because of a bad song. There were a few really bad CGI scenes as well. Rounding all this out my rating is a 5. Most of that rating is because of how much I loved Gwi. However, I will say that once I accepted the fact that this show was going to be a bit silly, I found myself enjoying it.