I have been a halo fan since 2008, the late halo 2 days. I have every game and every book, and all along the biggest mystery has never been revealed. The Forerunners. Why did the massive weapon, halo, have trees and wildlife? How did the Forerunners disappear so suddenly? This book had answers to many, but not all of, my questions about them. Of course, other questions will no doubt be revealed later in the series. Finishing this book left me wanting more.
The first part of the book was quite boring, and I left the book to gather dust. A month later I picked it up and read two or three chapters, and the good part started. I couldn't put the book down.
The book revealed new things, too, like the precursors the mysteriously extinct advanced society that came even before the forerunners, as well as the flood's origin story. I would recommend this book to anyone that likes sci-fi, halo fans or not.