MaddAddam at its best is a story about storytelling. Toby from the previous book takes over Snowman's role as storyteller to the genetically engineered new humans called the Crakers. She tells them stories about Zeb, the leader of the MaddAddamites. We readers get Toby's mythologized versions of Zeb's story for the Crakers benefit as well as Zeb's own much less bowdlerized versions. Through these stories we see how the stories of ordinary people can become legends, which in turn can become myths.
In this third and final volume we get the remaining backstory of Zeb, his brother Adam (Adam One) and the founding of the God's Gardeners. There is also quite a bit about the pigoons, pigs genetically engineered to grow human organs for transplants which as a side effect have developed near human intelligence. Attwood tries for some humor in places that doesn't always succeed. She manages a fairly optimistic conclusion for a post-apocalyptic novel. That said, if you can get through the final chapters without a lump in your throat you are a harder man than me.