There are so many things disturbing about this comic that one is pressed to single one out, but violence is definitely at the top of the list. The merits are many, starting with the writing, pencil work, the coloring, the layout and sequencing, etc. In other words it has all the elements for a great comic, but just too much violence.
Millar does an spectacular job at satirizing contemporary super-hero comics to the point of making a definite statement about our pop-culture and where we are heading: its a cautionary tale; a prophet in the wilderness crying out to the rest of us what comics have become. This is great stuff.