I liked how the Culture Minds schemed against each other, in the setting of the sudden appearance of a mysterious space artefact that even the superminds had trouble understanding. But with long, random names and lack of characteristics made the "back channel talks", between the Minds, really hard to follow (without taking notes).

The human/alien characters had more life though and their parallel plot was equally interesting and easier to follow.

I was kind of suprised at the near end reveals of both plots and how everyone got a happy ending.