Somewhat off-topic, but I just couldn't get into the second book, whereas I loved the first book.
I think it's because Children of Ruin didn't have as much of the way relatable human (or Human, as the book goes into) characters to latch onto as an anchor while they explore the evolution of a different kind of intelligence. I was really rooting for some of the human characters in Children of Time, namely Lain, whereas Children of Ruin just felt a little too, uh, alien.
Was wondering why I had to scroll this long for this to be recommended.
The two books in the series are both fascinating for trying to imagine thinking in the manner of another species evolved to be "human level intelligence."
I enjoyed the first book more, but the second does an admirable job exploring what communication, thought processes, and technology look like from an octopodes perspective.
To this day I wonder if consciousness is needed, or a hindrance for intelligence. That is that SF is all about, raising and play with these kind of questions. Can truly recommend Blindsight.
It's worth to read all of his 'first contact' themed ones. They all use a slightly different lens on the same theme:
Eden, Solaris, The Invincible & His Master's Voice
[1] https://en.wikipedia.org/wiki/Fiasco_(novel)