The Year of the Flood isn't really a sequel to Oryx and Crake like I expected it to be. The two novels' events happen at the same time: the plots and characters are interwoven. The Year of the Flood is narrated by two of these characters, Toby and Ren. They're both part of an environmentalist group called God's Gardeners. The novel jumps around in time between Year One, when the God's Gardeners first organize, and Year Twenty-Five, when the Waterless Flood knocks out most humans. The Waterless Flood is the virus Crake intentionally spreads in the first novel. Then Things Happen, as they did in Oryx and Crake. We hear a bit more about what happens at the end of the first novel, though not much. Many of the characters in The Year of the Flood are minor characters in Oryx and Crake, and vice-versa, which makes it interesting.
I think I liked The Year of the Flood more than Oryx and Crake, though that one was good, too. I gave this one four stars on Goodreads because, unlike Oryx, it's really preachy. Explicitly so, even. The way Atwood does it, though, isn't annoying, at least for the most part. Adam One, founder of the God's Gardeners, gives sermons of sorts, followed by poems Atwood says were inspired by William Blake's poetry. You can listen to some of them here. They're super-corny.
I explained my past with Margaret Atwood in my Oryx and Crake post, so I won't talk about it again. These books, though, have reminded me of how much I enjoy her stories and her writing style, so I'll revisit her novels soon, though only after some DeLillo because I've given myself a stern talking-to about the Thesis Monster situation, and I have to get to work.