I like how the setting is just the grimmest apocalypse imaginable. In a regular zombie apocalypse I could see myself trying to make a go of it, see how long I last, find a bunker or a farm or something. In a Crossed apocalypse, I'm reaching for the nearest gun and blowing my head off immediately.
Some works like The Road are comparably grim, but 99% of the population turning into sadistic maniac rapists is just the cruelest.
90% of Crossed stories are just terrible, mind you, but the setting is fascinating to think about.