Read this coz I read your reviews here, thanks.
I would argue that Lemire doesn't really tie things up, and we KNEW he wasn't going to be tying things up since Book 5 came out. Book 5 basically kicked the can backwards as far as the reason or the explanation for the plague, and in Book 6 Jepperd basically says something like "we don't know, we'll never know."
A little disappointing, when for four books, Lemire was dangling the answer to the why question.
We do of course get a conclusion for Gus, and a long-range one at that, so it's not like Lemire totally reneged--and I'd still recommend the entire thing to anybody--just for the world-building.
But he doesn't tie things up--in fact he goes out of his way not to.