A secret Italian organization rescues seriously injured little girls and condition them to be assassins. That pretty much sets up the mood and direction of the story. Each girl is paired up with a middle-aged man who is the trainer/owner of the girl, and they form a fratello unit. The series revolves around the relationships between each girl and her trainer, and the sad past and experiences of each of these girls. The series reminds me of novels like 1984 and The Demolished Man, where the creator seems to want to make a point about conditioning and brain washing. We can look into the minds of the little girls and find out their own perspectives on their conditioning and how well they cope with their determined short lives. We learn that despite the girls' total acceptance of their fate and have discipline like a soldier; they cannot help being adolescents in their hearts.
Of course, the anime isn't called Gunslinger Girl for nothing. Bluntly, these girls know how to kick ass. The protagonist girl Henrietta carries an Italian made P90 machine gun and stores it in her violin case. The way she reloads her clip, the realistic sound and the recoil of the gun made the action scenes no less than extraordinary. There are bullets whizzing by and blood gushing out of shot people. The unique weaponry of each girl makes the girls look like the SWAT team, and in a sense that is what they are. Too bad there are very little action scenes, so unless you appreciate the psychological theme of the story, you are not likely to enjoy this anime.
The art is fair and there is nothing special about the music, except for the rather enjoyable end theme sung in Italian. The ending of the story is understandable, but it does not serve as a satisfying ending for me. Some people argued that the ending isn't an ending at all. My suggestion is to watch the first three episodes, if you don't like it, stop because it is not going to get any better.
High: Really good action scenes, realistic gun fights. Sad little story.
Low: No spice, the flow of the story is too boring and serious. Better off as a novel.
Bottom Line: If you are attracted only by the idea of girls with guns, you are going to get disappointed.