After seeing it on the list in this thread, I decided to read Annihilation, and I just finished it. As others said it's weird (I like weird, so it's one of the reasons I wanted to read it). The writing style really reminded me of H.P. Lovecraft, which is to say it's a bit stilted. I'm glad I read it - it's an interesting world and the story is told in an interesting way - but it's not a book I'll recommend to a lot of my friends. Some of them, maybe.
Annihilation is a good book, but the hype it got is much more due to:
the fact that it arrived at the peak of the new wave of interest for Weird lit,
its (again, very timely) environmental spin to weird fiction,
the fact that Vandermeer worked a lot to present himself as THE authority on Weird fiction, with his articles, collections, prefaces to reissues of older books and so forth.