Well, at the end of the day, that's what this drama boils down to. Ahn Jae-hyun was a cute looking vampire. I wasn't expecting much from it to start out with, which I feel is the right way to approach anything vampire-related that is not "Train to Busan". Was I entertained? Yes. Was it GOOD? No. Did the end make any sense at all? NO (spoilers at end). My mostly coherent thoughts about this drama:

The medical aspect of the drama was pretty captivating, particularly as they begin understanding the nature of the virus, its origins, and how it mutates. I'm not a medical doctor, so most of it went over my head, but it did make the drama seem smarter that it probably was. I'm very easily impressed when I first finish a drama (because I try my best to get into the story and character development) and my personal notes say that the ML had good character development and that the music matched the theme well by being appropriately dramatic.

Notable characters:
- I'm still not sure how I feel about Ahn Jae-hyun's acting chops, but he looked pretty good as a broody, yet soft, vampire who wants revenge for his parents. He does seem to do a good job at balancing between hot shot and goofball (like with the "expensive glasses" he makes a big deal about that were easily replaced with some street knock offs)
- Ku Hye-sun was bearable in it. I found her completely obnoxious in Boys Over Flowers, and she had much better chemistry with Ahn Jae-hyun than she had with Lee Minho, which makes sense since she married AJH a year later. Their relationship turned from hate to love pretty quickly, but at least you could buy into their attraction.
- Jung Hae-in was great comic relief with his mothering of the ML, and robot antics.
- The two main villains (director and uncle) are both pretty hateable, so I guess they accomplished their roles.
- Intern was pretty bad ass as well.

Ending spoilers (my take on the ending that made no sense): I'm assuming this drama ran into the same type of problem that many kdramas encounter. For some reason, they either run out of money or time and need to rush the ending. After our vampire hero presumable dies on the rooftop, FL makes a trip to Romania. As she's about to get attacked by vampires, Ahn Jae-hyun's character pops out and somehow he's alive and saves her. The possibilities are that some other person saved her and she's imagining it's him, or that he truly did survive. My take is, he somehow survives the sunlight in the rooftop (why did she just leave him there then?? who knows), but had an extended period of recovery (again, why he didn't reach out?? who knows.) After his recovery, he follows her to Romania where he saves her. They live happily ever after.