Hits hard from the very beginning and keeps on hitting. Three hundred pages of cruelty; suffering; the very worst of humanity. Brief moments of respite, in each of which our heroes pause, catch their breath, wonder whether they're safe at last. (Not-much-of-a-spoiler alert: they're not). Further suffering ensues.
I found it heavyhanded at times— then again how could it not be? — and the writing uneven: beautiful at times, a slog near the end; but maybe that was just me. Like other books I've read recently, the reader is kept at a distance, but with third-person narrative that distance feels clinical, objective, not uncaring; the absence of connection coming out of self-preservation, a necessary response to a lifetime of loss.
The "railroad" gimmick didn't really work for me, but it was a minor plot point overall, unobtrusive.