If you are anything like me, you loved the mystery and suspense of the first book, Annihilation. You found the second book to be an unexpected and frustrating experience, where the mystical Area X is abandoned in favor of a a boring, tedious political drama. You are here now, considering buying the third book, seeking answers and closure. You will not find them.
Bewilderingly, 60+% of the book is dedicated to the mind-numbingly boring day-to-day routines of two characters whose stories are almost completely unrelated to anything you actually care about. You will spend page after page reading about random townies drinking cheap beer in a bowling alley. An old man befriends a young girl and watches wildlife. Control spends countless hours daydreaming about his mother and grandfather, again.
The little action you do see is interesting, but doesn't come close to answering any of your burning questions, nor does it take the story in any remotely interesting direction. It's all just more random wandering, random bizarre encounters, random mumbo-jumbo lines like, "he listened, but did he really hear?"
The best thing I can think to say about this book is that your journey through it will parallel the characters surprisingly well. Everyone sets out in search of answers, in search of meaning. They are beset immediately by frustrating, pointless problems and personal disputes. Eventually the weight of it all just becomes too much, and they each give up in some way. The best possible outcome is to come to a sense of Acceptance—there are no answers to be had, to meaning to any of it, no morals or heroes or memorable stories. It's all pointless and futile, it's been that way since the beginning, and you're just glad it's over.