Another case of an anime that feels like it ended too early. The weakest aspect is definitely the unfinished overarching plot, as well as the art and the animation. There is a lot missing. Things that "should" have been explored, considering the premise and setup, but weren't. This is because the show ends at volume 5, while the manga is 15 volumes long. The animation quality takes a nosedive sometimes, especially early on in season 2, like during car chase scenes. Season 2 also commits the sin of overusing flashbacks. My guess is that the studio ran out of resources and/or time during production, so they cuta lot of corners in the visual department and ultimately didn't finish the story.

The anime's strength is in the writing and character dynamics. You empathise with the characters, or at least want to know where the plot takes them.
Season 2 doesn't rush through character arcs as quickly as season 1, but still dedicates entire episodes to secondary characters or specific character developments. Season 2 also introduces a major villain, but tries very hard to make you not want to see the villain lose, similar to how season 1 focused on making everyone morally dubious or pitiful in some way.
Even if the anime sadly doesn't show you the full story, it definitely makes you want to know how it ends. If the goal was to make you want to read the manga, then it is a success I guess.

Overall, Gunslinger Girl season 2 is just more of the same. I rank both seasons with an overall 7, because they're definitely above average, just lacking in visual quality and story progression.