Ennis has an eye for tough guy characters, and is suited to writing the story of this iconic character. Sure the violence is over the top, as Castle blasts his way through masses of bad guys, and how many times can he be wounded and get up and continue the fight. But the story flows, and adding the international angle with the expected amounts of politics, dirty deals and corrupt individuals helps to show Frank's moral core, and unwavering belief in what he is doing is right.
Look for the trade paperbacks as each one collects a storyline and break the run up into chapters.
Also Ennis's version of Fury is a lot of fun as he is in pure bad-ass mode.