I really enjoyed Darker Than Black - Kuro no Keiyakusha. Matter of fact, it's one of my all time favorites. So naturally, I thought I would enjoy this one.
The reality is: I didn't. This is unfortunately due to the change in roles of the characters. I continued to watch it through (Am still watching as I type); just for the love of the background story and settings.
This one gets a low rating from me, and without giving any spoilers it's mainly, again, due to the change in roles of the main characters from one chapter to another.
If you abolutely love the story line of the contractors from Kuro no Keiyakusha then you may want to stick with this short 12 epi anime to get more of that story line. If you didn't like that background and setting; then I suggest you skip this one.