The series' relatively low rating surprised me at first but I may know what's the reason behind it. Suisei no Gargantia is more eclectic genre and theme-wise than most mecha anime, adding social and ethnological layers to the setting and interspersing the story with hard sf elements (especially the intellectual evolution of Chamber AI comes to mind as an example). The key features of the series are the "stranger in a strange land" element of cultural adaptation, the main character's inner evolution and the theme of utilitarian utopia represented by Gargantia. Therefore, SnG demands some flexibility from the audience it is addressed to.
Wonderful music, great pacing and coherent story is what makes this series extraordinary. Some may criticize those few mild fan-service moments in this - rather serious - sf tale, but it just made it more varied and enjoyable in my book.
