I think Banks wanted to write something of a critique of late stage capitalism (Culture novels in general being a variant of Space Communism). Unfortunately the villain is a bit too much of a parody for my taste. I also found the first third of the book a bit of a slog, as the various in-Hell plot lines involve a fair amount of gratuitous violence and suffering, and don't obviously go anywhere.
That said, I did find the last 2/3 fairly engaging and fun.
I suspect people who are sensitive to the portrayal of sexual violence should not read this book.