I finished No. 6 a couple days ago, and I was not overly impressed. It left me with a, "That's all?" type of feeling, and I felt that too much vague background story was rushed through in too few episodes, and I was left with many unanswered questions, most notably, "Is Nezumi male or female?" Unfortunately, it didn't hook me enough to want to read the novels (if they are even translated).
I will say, though, that I did like that No. 6 revealed information through the story and characters' actions and beliefs, instead of "telling" via long, obnoxious monologues and ill-timed flashbacks.
^Yeah, I was kinda disappointed. All the subtle character exchanges and intriguing plot points of No.6 were built up only for the show to fall apart once the ending came round (imho). With one season shows like this, it seems rushed, over-the-top endings are a foregone conclusion. I love Bones and noitaminA, but sometimes they bite off more than they can chew.
And I'm pretty sure Nezumi's male, but y'know, can't be so sure with these bishies!