Actually, I'm a little annoyed because I thought 'Malorie', the sequel novella, would clear things up, but it really didn't. It's set after the events of the first book and follows Malorie's life with the kids, but it barely expands on the creatures themselves. We get a tiny bit more about how the world has sort of adapted, but the core mystery of what they are or where they came from is still totally untouched.
It feels more like a character study than a plot-driven sequel. If you're looking for concrete answers about the entities, their origin, or the rules of their effect, you'll be disappointed. The story is more about coping and moving forward in a broken world, which has its own merit, but it doesn't satisfy that itch for cosmic horror explanation.
Honestly, I liked spending more time with Malorie and Tom, but I finished the book feeling like I'd been blue-balled on the lore front. It's a decent read if you just want more of that survival atmosphere, but don't go in expecting revelations.