Gut-wrenching. I think what broke me most is that even though the book already starts in a post-apocalyptic world, with societies institutions pretty much completely broken down, Lauren (the protagonist) spends the first half of the book talking about having to prepare "in case it gets bad". As another character puts it: "We haven't hit bottom yet". But as bad as it gets, the story provides at least a glimmer of hope, in teaching the merits of mutual aid.
It's too bad Butler didn't get to continue and finish the series past the first two books. She clearly put down the seeds (no pun intended) for a pretty epic, millenia-spanning story. I wish we'd get to read it.