Let me just say up front: if you’re looking for a resolution, a concrete simple answer, this isn’t the book for you. I think that’s the point: VanderMeer gives us the uncanny, the unknowable, the impossible, and posits that maybe when we come across alien life we’re not gonna know what the heck to make of it. That we might not see any rhyme or reason in what they do — that to us, there may not be any rhyme or reason.
If you’re looking for solutions to some of the smaller mysteries, like what the creation of Area X was like, or why Saul Evans is involved, or anything like that, there’s some of that here. You can find out what happens to some of the characters, like Control and the biologist (though Grace and Ghost Bird are less certain). You get a lot more mystery, atmosphere, weirdness — basically, more of everything you’d expect if you’ve read the previous books.
And I don’t know about anyone else, but I found that I’d got quite attached to the characters. I cared about Saul Evans and Charlie (and excuse me while I’m incredibly pleased about the casual gay couple); I cared about what happened to the biologist and to Grace; I cared about Gloria/Cynthia.
Overall, this is a brilliant trilogy for the pure atmospherics of it. The weirdness. The sense of place. The actual real alienness of Area X, and the paltry efforts of humans to understand, define, dissect it.