Yes, I am being biased for this. However, this is the sort of anime, which execution is so crucial and it is so well done.
The story is creative in the way it portrays the vampires. But what is essentially compelling about the story is its exploration about what it means to be human. The story forces the characters to make difficult decisions and often morality and survival are at odds. This is a very well written plot that was brought to life by very good directing.
The characters look good and the music is very well suited for the scenes.
You have a mix of characters and as with such stories expect their core personality to breakdown and react to the situation. It is sadistic but enjoyable to watch the characters evolve through the plot.
Vampire thriller, what is there not to enjoy?