What more can I say that I haven't already said about this series? I've been singing its praises for the past 3 volumes and with this 4th installment, it shows no signs of slowing down.
Rodriguez really shows off in this collection. He clearly isn't satisfied in sticking with the artwork that has made this such a great story. He takes a bit of a risk within the first chapter and transistions to a style similar to Calvin & Hobbes, which despite the darker subject matter, still works.
While more than a few things happen in this volume, the story never seems cluttered and nothing feels unnecessary. The introduction of 3 more keys lead to several twists and turns as well as some pretty awesome scenes. Probably the biggest twist in the story happens near the end of this book causing me to salivate for the next release.
I'm hoping that when this comes to an end (a sad day, indeed), they decide to group this into one massive trade. As of yet, there are no weak points or bad developments. In my experience, it's rare that a 4th volume is just as strong as the first. It takes a great duo (writer & artist) to pull this off. Rodriguez and Hill falling second only to Brubaker and Phillips in my mind.