At first I thought this was a horror story because of the vampire theme, but vampire activities play only a minor role in the story. After getting over my initial shock at the main character's blood obsession, I saw many other themes playing prominent roles in the story. Relationships, independence, romance, forbidden love, depression, suicide, and death are the true masters of this world.
It is striking how few times anyone smiles, or looks happy in this manga. Every event is an excuse for depression, crying, and hiding for the characters. The one word description for this story is probably emo.
It isn't all bad, since I did like the art quite a lot, and Chizuna-chan is drawn especially beautifully. The story seems somewhat original, though it does't do anything too surprising. I was able to relate to most of the characters, and even feel a bit of sympathy for them. So it did keep me reading, and I was somewhat satisfied at the end.
I would recommend this manga to fans of Psychological, Josei, Seinen, and Tragedy. I disagree with the genre tags applied to this series here at MangaUpdates. Not recommended if you're looking for Horror, Supernatural, or any Action.
Edit:
I've now seen the anime OVA, and it made me appreciate the manga even more. The anime is surprisingly true to the manga in most respects, with only one major change that didn't really affect the outcome anyway. The last chapter of the manga is omitted completely, and much of the story is compressed to make it fit in only 4 episodes. Still good, and recommended to fans of the manga.