Imagine some kind of zombies that become cannibals when infected but retain a certain intelligence (but are completely mad).
Imagine scenes of raping (male and female), children dying in really gross ways, hard-language and terribly cruel situations.
Then you can start to picture how is Crossed.
It is good, but really not for everyone, I thought Walking Dead was hard but compared with this comic it is nothing. But if you're willing to, it is not badly narrated and contains some disturbing but imaginative "survival ideas".
The flashbacks are not perfectly placed and sometimes you need to read one or to pages to notice it switched back to the past again. The ending part was neither bad nor incredible but overall a recommended reading.