Story is quite captivating, it seems fresh to me (I have watched only one more vampire anime, though), but having watched it all I realize it's rather basic and predictable when you know enough. The good thing is the atmosphere of mystery holds quite long and there are revelations even in the last ten episodes.
That said, some were ridiculously obvious and also literally delayed for tens of episodes without any reason behind this. The story is also extremely dragged and sometimes feels like not moving at all. I think the number of episodes could be halved to make the plot develop without periods of nothingness. The story feels somewhat disjointed between different countries, as well. There is also the Schiff subplot that feels detached and doesn't really affect the main plot in any way. And there is a lot of plot armor and everyone is able to talk to everyone in Japan, Vietnam, France, Russia, the UK or the USA.
Art: 4/10
The artists seem to have done some research, I was particularly glad to see the setting of different countries displayed accurately. Still, the art style is somewhat unusual and I couldn't help thinking character designs were way too cartoonish and undetailed for an attempted dark atmosphere. Often, when one shot changes the other, so much happens it can give you a feeling of some shots being dropped somewhere.
Sound: 5/10
Mainly fine, but I find Saya's battle screams and Kai's angry voice terribly annoying (Saya screams 5 times or so, but Kai spends all first half of the show angry and yelling). I liked the cello music Hagi keeps playing, but it happens rarely and he seems to be playing the same moment every time. And the characters tend to say other characters' names all the time, in any circumstances, even just because.
Characters: 2/10
That's the real problem with this anime. Protagonists are mainly useless. A useless main heroine Saya who only feels sad, avoids any help and communication, saying she has to protect everyone, sucks in fighting (she's usually unable to fight 3 ordinary chiropterans in a row) and doesn't do a single thing about it, all because she resents her nature. She's still the only one who has at least theoretical ability to defeat chiropterans, so we get the only one capable soldier being terribly indecisive (kinda like Shinji from Evangelion). A useless secret organization who has a sweet didactic talk with too nosy a reporter, sinks a ship attacked by flying creatures to bury them and keeps sending people against chiropterans, the monsters who are bullet-proof and able to tear a human in 2 seconds. I wonder how this organization even managed to exist for more than a century. The useless adopted brother of Saya, Kai, who's whiny and slightly sabotageous in the first half, he at least stops shouting in the second, but, unfortunately, doesn't become much of an asset. Hagi, Saya's chevalier, is somewhat useless, constantly being thrown somewhere or impaled by enemies and vainly fighting back. There is a reason behind his rather little fighting capabilities, but given the scale events attain, I think it's plain stupid. Also he can't really think on his own and only waits for Saya to give him an order, while other chevaliers built a multinational corporation on their own. I guess, "Nankurunaisa" or "The things will work out" is mentioned this often in-universe because it turns out to be the motto of the protagonists. They don't work toward their victory, they just wait around with sad faces and suddenly start winning in the end just because this anime has to finally end. There is also at least one situation of stupid inability to express/perceive one simple thought (whether one of the groups is a total enemy or can be negotiated with) for the sake of cheap drama.
The antagonists aren't useless but are ruthless and/or psychopathic. Solomon, though, is particularly prominent, because he's a thoughtful character with interesting development vector, but his development also stops just when there was a good prospect, without him really achieving anything.
The side characters or the guys somewhere between protagonists and antagonists either are underdeveloped or are finished soon enough. Looking at the characters in focus, I'm just happy they aren't ruined as well.
In the end there is simply nobody to root for or care about but annoying Saya and her team are constantly shoved into your eyes.
Enjoyment: 1/10
The series starts rather promising. There are mysteries to be solved, the power to be acquired and the circumstances to be overcome. Saya is said to "not be fully awoken" which holds her back in battles and gives her depression and frustration. But as the story progresses, her abilities don't increase and the sadness doesn't go away which becomes increasingly annoying. The mysteries, on the contrary, get solved so the only reason left to watch becomes to know how it all ends. There the dragging begins... Luckily, it contains a period of quick pacing, but not in the end. Also the future events become increasingly obvious toward the end and the story degrades into simple killing of kinda villains of the week one-on-one with luck and miracles. And the attempted depressed dark atmosphere is based not on the real events but on the mood of the main character I could care less about. So we get 50 episodes of Saya whining, shutting in and getting her ass kicked. It's a marvel the "good guys" are able to last this long. There is also a lot of blood, more than I expected or wanted, but I guess it's on me, given the name of the show.
Overall: 2/10
I feel sad I spent my time on this and I definitely won't rewatch it. The story isn't that bad and the abridged version of the plot would read cool, but watching it for 50 episodes, as well as horrible character stupidity is just a waste of time. It's not what you expect from a show with this lot of praising reviews here marked as helpful.
