A new character, Control, brings a new viewpoint in the wake of Annihilation.
This book is largely about the organization that “manages” Area X, from the POV of a brand new director. Even on the “right side” of the border, everything is odd. As the book goes on, we learn more about the conditioning techniques that were applied to the expedition members.
In the end, it’s a sequel in topic–but with a new vantage point and different focus. In the background Area X still looms… but we now get hints as to the dysfunction that was involved in running it, the effects of being near the border, etc.
If you enjoyed the aura of mystery in Annihilation, you’ll probably enjoy the continuation of the story in Authority.