Although Annihilation was on the shortlist for best SF book on the 2015 RUSA Reading List, the tone is more horror, a creeping dread of threats internal and external. There are comparable SF works (the movie Sunshine came to mind at times), but it's also quite Lovecraftian. Not only am I not sure what happened at times, I'm not sure how sure I'm supposed to be of what happened, but I was engrossed even as I was confused and the other two books in the series are already out, so if time allows I intend to continue reading and see what answers may come.
Overall: B+