I've been digging Criminal by Ed Brubaker and Sean Phillips since the first issue. The second story arc [Criminal #6] has just started and it looks to be even better than the first! Since it has new characters and a new story, it's the perfect jumping on point! Tracy Lawless is ex-military and AWOL. Already prone to violence, Lawless is after his brother's killers and nothing is going to stop him from getting his revenge.
Brubaker and Phillips are responsible for one of the best comics published today and I can't recommend it strongly enough to mature readers [due to the language and violence -- you can probably tell that I edited out some language in one of the panels above].
Criminal #6 rates an A+