I thought the general idea was very interesting. I always felt that there were too many shows/series with men being the hero so it was very refreshing to see that this time, the heroes or should I say heroines, were not just female but little girls! (Even more kickass) I really liked the idea of killer little girl assassins which was why I was kind of disappointed at the lack of action in the anime. I would have loved to see more of the girls in action although I can understand the need for delegating airtime towards introducing the viewer to their daily lives and such.
I also liked that the background music featured lots of classical music. I felt that it was appropriate since the story is set in Europe and I also feel that it adds a nice touch for the more intense scenes.