3.25/5 stars. 
 The New York Times review of this book labeled it as being "compulsively readable,"which I reference here because it's the thing that immediately comes to mind when I think about the fact that I read this 1000+ book in two days. 
 I'm just not sure that actually makes it a good book. 
 What I liked: 
 Cronin's writing is accessible and engaging. The man writes some great action scenes, which is a large part of what makes his books so readable and exciting. It's likewise obvious that he very meticulously and carefully works through even the most minor details of plot and character. For example, we get a very involved backstory of the main antagonist; I've also learned more about ship re-building than I ever thought I would. 
 The scope and world building are, as always, impressive. We learn more about the virus, how it mutated, how the rest of the world was affected. We visit a variety of different locales (on this world and some other, more nebulous one) and see how society progresses from the end of the last book to literally 900 years later. There are a few things that I feel like were left purposefully dangling, so there's always a chance Cronin adds more to this world, which would be fun. 
 Finally, I was worried that the gap between the books would me feeling lost or disconnected from the characters, but Cronin does a good job of catching the readers up in a way that actually connects with the overall story. His characters and world likewise feel natural and lived in, so it's quite easy to reconnect with both the story and the cast of characters. 
 What I didn't like: 
 The antagonist. Timothy Fanning aka Patient Zero was really underwhelming. When Amy finally meets him, she describes him as somewhat pathetic, which is how I felt about him as a whole. In the middle of the book, we're given a momentum crushing section that recaps his life from the time he's 18 up until he becomes Zero. I'm not sure if this long section was meant to make us sympathize with him, but mostly I found myself irritated. I It basically boils down to this: (view spoiler)[ Entitled Harvard grad decides to destroy the world because life is unfair and love hurts (hide spoiler)]. 
 The treatment of women. There's quite a bit of abuse against women, all of which doesn't really add anything at all to the advancement of the story. I suppose Cronin injects it into the story to show how strong the women are, but I feel like he could've showed the strength of the women without resorting to having them be raped. Also, (view spoiler)[ I really, really, really hated the way Alicia's story ended. I thought it was totally out of character and also just generally upsetting. (hide spoiler)]. 
 Amy and Peter. I was really not a fan of the trajectory of their stories in this book. (view spoiler)[ Maybe this is my fault - I've sometimes been described as being very oblivious - but the idea of them being romantically linked kind of squicked me out. I spent almost two whole books thinking they were not going to be romantic, although I had some inkling that it was going to be that way from the end of the last one. I know that she's actually super old, but the fact is that when he met her she looked like an actual child and then spent a lot of the last book looking like a teen. So him telling her "I think I've always loved you" was all sorts of weird and vaguely creepy to me. I also really hated that she couldn't let him go at the end. I understand that she really loved him, but resigning him to an existence where she had to remind him who he was every night seemed cruel and selfish. (hide spoiler)] 
 Finally, as I mentioned earlier, Cronin very obviously gives a lot of thought into his world, plot, and characters. I'm just not sure if including all of those meticulous details was necessary for the book. Sometimes, things just seemed rather tedious to include. 
 On the whole, though, I am glad that I read this book, if only to finish up the trilogy. Like I said, the world building and scope were really well thought out and well-written, so it was still quite fun to dive back into this world one last time and see where the characters and storyline went.