A bad anime with a plot too interesting to skip it. Don't rely on the marks I have given them, but read the review itself instead, since the series can't be rated easily.
The animation is simply bad. Lots of still scenes (people walking while the background doesn't change at all), characters mouthmovements don't fit with the voices, and they contain unrealistic movements sometimes. The backgrounds look just plain and not creative at all, as if they don't have any role and the characters aren't even supposed to have anything to do with the background.
On the other hand they have chosen for bloody scenes without any censorship at all. Also, they don't seem to use re-used frames, which is also a good thing. And the characters look okay.
The OP/ED are nicely done, but imo not really outstanding. The voices are done nicely, but they tend to get a bit annoying sometimes when they yell out to someone. Still, doesn't happen too much, so I won't distract points for them.
The voices do fit the characters though, which is a good thing.
The story is a bit bad, but the atmosphere makes up for a lot, even the bad animation. This series distinguishes itself from others by shock--effects; people can actually die in this anime, giving this anime a very high unpredictability and therefor making it a lot more interesting.
Although the overall dialogues are a bit cliché sometimes and the plot lacks solidness every now and then, it's still interesting enough to keep watching due to the atmosphere.
The characters are, like all the rest of this series, varying. Characters like Sena and Todo get a lot of development in the beginning, while the ending focuses more on other characters. Unfortunately some characters don't get any decent evolvement, while others are developed in a very good way. It's hard to give a general mark for all of them.
In general, the atmosphere is a bit mystery/detectice-like, with a sort of actionhero-feeling because the characters are all part of secret organisations and such, making it all a bit less realistic. On the other hand, the suicides in the beginning of the series have a great influence on the mind, especially with the 'Führer'-thing around, giving you a feeling of a huge facism-underground. It's hard to say more without spoiling more of the story itself.
In the end, you cannot rate this anime on points like this. The story is lacking, but the atmosphere is so intense that you keep watching. The characters are sometimes developed very well, while at other times, some charactrs don't get any development. The animation is good for the characters, but horrible for the backgrounds.
The realism is very present in the fear and the characters, while it's completely unrealistic at things like the 'secret organisation' again.
And while the series had a good bunch of characters and mostly good developed ones, the series gets 3 times more characters in the last 3 episodes, making it feel like you're watching an overdone action-movie.
At last I want to say that this anime doesn't seem to care about the audience. They use pretty shocking scenes for an anime, and together with the intense atmosphere this can give you a creepy feeling. Killing people, messing with the minds, nothing will be left out.
So if you like psychological mystery, then this might just be the anime you want.