I was introduced to this series by the anime club at my university, which I rarely go to. I must say that on this occasion, I'm so glad I did. I love this series, and if you like things which are darker and somewhat disturbing, I'd reccommend it.
This is a series where the protagonist faces a very real risk of dying at every corner - it doesn't come with the gurantee of a 'hero saves the day' ending. That alone makes it stand out against some other series. The cast of characters is varied and often they surprise you. I have also read the manga which this was based on, and can say that personally, I am not a fan of the story after the anime ends. That being said, the ending to the anime does make me wish to see more..