There's only one word to describe this graphic novel - disturbing
It's not good, it's not bad, it simply exists. I've read plenty of end-of-the-world scenarios, and none of them are cheerful. Crossed just takes it too far. I don't think you need to read it, in fact, don't. There's nothing in it that will be memorable apart from the hideous amount of extreme violence.
Halfway into the book, when the "crossed" are eviscerating a child while raping her parents, I caught myself wondering why I was still reading it. It felt like the author was saying "You think The Walking Dead is screwed up? Well check this out!"
You should read this if you are a budding sociopath, it will make you feel moderate.
You should not read this if you are a person.