I disagree with the reviews that say questions were left unanswered. I mean.... was there a concrete, tell-all explanation? I guess not. But the author states that, even for those involved, understanding what was going on was a stretch for human imagination. He gives the reader way more than I expected. He lays out exactly what caused Area X and why. He explains most of the mysteries of Annihilation. Elements that remain vague feel appropriate to the understanding of the characters at the end.