Children of Time is excellent, and does a really good job of tracking the evolution and eventual ascension of the Portiid spiders. Tchaikovsky creates a really convincing civilisation based on the limits of the planet and the spiders: a technological civilisation without major metal use and with nearly perfect information transfer between generations.

The sequel Children of Ruin was a disappointment. It came out recently and I bought it straight away. I'm fascinated by octopuses, but I felt their civilisation was given short shrift to make way for the rest of the story he wanted to tell