*This is a review for Ennis' entire Punisher MAX series. I won't cover future volumes individually, because of time restraints*
Some comics writers, when tasked to write a popular character for either of the big two (Marvel, DC), deliver such a powerful iteration of that character that other interpretations instantly become either redundant or just plain silly. This is most certainly the case with Garth Ennis' epic Punisher MAX series (2003-2008). Needless to say, I was as merry as a pig in shit when Marvel announced it was going to reprint the whole thing in affordable softcover collections. To me, it is still the most potent version of Frank Castle (aka The Punisher) ever devised.
Ennis, from the very beginning (after the origin story "Born"), did one thing absolutely right with this run. Here, Castle is a Vietnam vet in his fifties, still operating in modern New York, and hard as nails after decades of wreaking violent retribution on anyone he deems deserving of it. See, in order for the character to be kept young (and to them, popular), Marvel editorial had a rather annoying habit of "updating" the war Castle was involved in. Completely wrong choice. Vietnam is very distinct in its feel and impact. Castle's involvement with it is absolutely key to his psychology.
Adding to that, Ennis greatly expanded the world of Frank Castle. The first 6 issues ("In the Beginning") is basically a sort of send-off for the opponents Castle had to deal with on a regular basis: the Italian mob. After that story arc, Castle encounters warring Irish factions, goes abroad on a special mission for Fury to thwart a corrupt Russian general, and takes an East-European human trafficking ring to task (in what is probably the finest story arc, "The Slavers"), among many others.
Variety, tight plotting, recurring, well-written supporting characters (The Punisher being a very dour, not exactly talkative individual, needs a strong supporting cast to keep it interesting) and, above all, a great understanding of the character is what makes this series truly phenomenal. The brutal, R-rated violence doesn't hurt of course. It's how The Punisher should be done, after all. It fits perfectly.
If you read only one Punisher run in your entire life, accept no substitute. Get this one. Now's the perfect opportunity.