Short review: for those who enjoyed Annihilation, look back and ponder what parts you were particularly drawn towards. If you loved the unreliable narrator and the strange otherworldliness of Area X, you might not like Authority. There is an unreliable narrator element still and we do learn some things about Area X but this is an unconventional book plot structure wise. If you are intrigued about the bureaucracy of the Southern Reach and what the higher ups deciding to send people on expeditions are thinking, you might like Authority, but do not expect anything about Area X to become more clear. 
 If you want more thoughts on Authority specifically, along with the trilogy as a whole when I get around to reading Acceptance, you can visit my book blog.