I came across this anime on accident actually. I got the first four episodes in a grab-bag at an anime convention, and since the whole series was around $20, I decided to buy it. I have never read the manga, but I still liked this anime. It's tempted me to buy the manga actually.
The character development was very well-done, and all major characters were likable. Lucia is a badass, and has a dark past, while Sumire is kind-hearted and innocent. The pacing is well done (imo) and the story did not seem rushed, until the end that is. I also liked the art style a lot too. It was simple, yet elegant.
The music is this series is also a plus. The opening theme was done by Aki Hata, and the ending is performed by Yosei Teikoku, one of my all time favorite music groups. The soundtrack, while not very large, is quite good, and thanks to the shortness of the anime, the tracks did not get old. The dub is also decent, and all of the character's voices fit them perfectly.
The villains imo were really lame, but they did not have much back story to begin with, save for Lucith the main baddy who does not even appear until halfway through the anime. Also, the viruses which are the monsters in this anime look cliche and uninspired, but that might be just the anime, not the manga. The ending was rushed halfway to hell, which gave me a very mixed feeling about this anime when I finished. (It was clear that this anime had a low-budget though, which isn't necessarily a bad thing)
Overall: If you are into bad-ass girls that wield guns and kill demons, then this anime is a good watch. The characters are well-written, and the interactions between them are interesting to watch. The biggest downfall this anime has is it's ending but other than that all the other problems are minor. There was not really any yuri though, which I didn't care about in the first place.