Middle volume, the eye of the storm? I think VanderMeer wisely steps back a bit and rebuilds, no longer in the maelstrom of strangeness in Annihilation, but in the mundane world, reframing the narrative as he goes. It works. I'm still finding this series as gripping as anything I've read in a while, without tipping its hand too far and becoming predictable, mawkish, juvenile, or any of the other things that usually push me out of horror narratives at some point. There's a very difficult balancing act for me. I want to know everything, the craziest details you've got, this is why I keep reading... but give me too much, or the wrong details, and the spell is broken, all those fascinating and mysterious details fall apart and disperse. Basically, if a story tries to entirely fulfil my demands as a reader, those demands are revealed to be idiotic. So far, though, this is holding together. Of course the third volume, the resolution, is the hardest of all to keep on course through. 
 Also, I have to wonder if this is just the best adventure story I've read in a while, or something more. I hope more. Lovecraft's dread of the unknown is an obvious reference point here, but I think Vandermeer has a more multilevel, non-xenophobic understanding of his world which holds much conceptual promise.