This anime had a ton of promise, but it just tripped over so many hurdles in the execution.
The Good:
The story itself was damned interesting. You've got a world where nearly every adult died, and almost all the children were abducted by vampires. It's the story of how one boy manages to escape captivity and manage to fight back alongside the human resistance. It's the makings of a great shonen anime. Seriously, we haven't seen a shonen action story with this much promise since Attack on Titan. Funny thing that I mentioned Attack on Titan, because this anime's story might as well be Attack on Titan, except with super-smart vampires instead of titans. That being said, this similarity didn't take away from the anime; what the story lacked in originality, it made up for in interesting plot devices, such as pills that could make the characters into super soldiers, at the risk of death. Overall, I liked the story, and I might speed my way through the Manga so that I can get a better look at the story.
The Bad:
Oh boy is there a lot of bad. Let me start off by saying that there was a lot of themes I did like about this anime, I liked the story, I liked the color schemes they chose for the uniforms (lime green and black go together rather nicely), and I liked the always present suggestion that the humans might be doing something so evil in the background that the vampires actually might be the good guys in comparison.
So let's start off here with the biggest problem this anime has: Pacing. This anime could have very well been 6 episodes long with the amount of actual content that it had. It seems like they really tried making this anime too early, before the manga actually made it far enough to fuel a real half-season anime. The pacing felt fine for about the first three episodes, and things were going as you'd expect them in the setup of the anime, but as soon as time advances to present day, the entire story's pacing falls apart, within about 3 episodes (not exact, I have no intention of going back to rewatch this show to figure out where this actually happens), the crew find themselves embroiled in a warzone, one of the few cities the humans control has been invaded, and they have to rush to the rescue. But there's one problem, there's no rushing, it's more like a calm stroll to the battle. There's no sense of urgency, it's like when you're playing a game with a railroaded main storyline happening in the background, there's technically a story going on back there, but the characters will get to it when they feel like it, which doesn't work that well for a TV show like it does for a game.
As bad as the pacing was, it was made even worse by what I imagine to be one of the lowest animation budgets for a headliner anime I've ever seen. Let me just say that short of straight to video hentai, I've never seen animation this bad in an anime. Nearly every conversation between two characters was a series of stillframes with moving mouths. Every "battle" was a slideshow of individual characters making shouting sounds and advancing towards each other and then stopping as their swords met, so that they could could animate their mouths in another series of stillframes. It's not to say that there wasn't action, the first three episodes actually had decent animation (5/10), but you can tell when their shoestring budget really ran out. Combined with the lack of pacing, the poor animation really killed any sense of urgency or excitement that you SHOULD feel in a shonen anime battle. A battle in this anime consisted of a handful of vampires standing on one side of a battlefield with a handful of humans on the other side looking menacingly at each other while their main character leaders talked at each other for minutes at a time, every once in awhile punctuated by a character remembering they have a special ability they can use to turn the tide of battle, being reminded of their futility, and then a quick return to the standstill.
Oh, and another thing, the writer obviously knows nothing about the military. A big point that the anime makes early on is that the main character is GOING to join the military to fight the vampires. So, of course, he does (right around episode 4) and the first thing he does is disobey orders, putting his squad in danger. In the real world, this would be a court marshal, and probable jailtime or other punishment. He gets a "strong" talking to, during which he disrespects his commanding officer multiple times as well as outright fighting with at least one member of his squad. At no point is there any real reason given as to why he isn't just kicked out, or better yet, locked up in the brig. This anime might have been a lot better if he got locked up in the brig long enough for him to reflect on his assholery (although it still wouldn't have fixed the awful animation).
Closing:
In short, if you like to watch powerpoint presentations, this might be the anime for you. If you enjoy main characters who spend the entire anime being insufferable assholes that don't understand the concept of teamwork, this might be the anime for you. If you feel like the combination of lime green and black is a sufficient reason to watch an anime, well, you probably have something wrong with you, but this will be the anime for you.
Don't watch this anime.