This is a tough book to rate. To say it is disturbing is putting it mildly. There are scenes of graphic, often sexual, violence that are difficult to see. And as this is a graphic novel (graphic being the appropriate word), you do see them. Are they entirely necessary for telling to story, or just for shock value? To some extent it is shock value, and the shock and horror and disgust created by the images has an effect on the story, so I guess it is also necessary for the story to be what it is.
The format is the basic zombie/infected set up, the mass outbreak coming out of nowhere as a bunch of disparate survivors flee for their lives. These infected are not dead. Bites or bodily fluids spread the infection almost instantly, turning the victims into ravening monsters of the worst kind, powered by the desire to kill and torture and rape and eat their prey. The infection also marks their faces with a rash that forms a cross, hence the survivors name for them and the title of the book. In themselves, the crossed are nothing new; they are an embodiment of the basest evils perpetrated by psychopaths and war criminals, just like the Reavers from Serenity/Firefly. But here we are actually shown what they do.
The cross can obviously be seen as a religious reference - especially as this is Garth Ennis, who has always been obsessed with Christianity and masculinity. Is it the metaphor for an antihuman religion brainwashing people into acts of depravity? Perhaps, but this seems rather too obvious. The reddish crosses on the faces of the infected actually made me think of England football fans made up with greasepaint, an in-joke which is, I'm sure, entirely deliberate. And there are jokes, there is humanity in here, which is what makes it worth reading. The survivors have to try and keep hold of their own humanity despite the horror, despite some of the things they do to survive. At the end, the book does close with a note of hope and beauty that is achieved because of - not in spite of - the horrors we have witnessed.
So, would I read it again? No. Am I glad I read it? I'll get back to you on that. Is it well written and superbly drawn, is it gripping and affecting? Without a doubt.
However, if you are thinking of reading it, be warned. This is the sort of book that was beyond the worst nightmares of the guy who dreamt up the Comics Code Authority in the 50s.