Poland has had a very long and complicated history, disappearing and reappearing from the map many times, and moreover possessing a constitution and respect for civil liberties unique to late medieval and Renaissance Europe.
Zamoyski does a terrific job of clarifying the events of this intricate story. He is particularly good at explaining why things happened the way they did in simple language that does not dumb down the topic (I know, obvious for a historian but often ignored), and what underlying historical currents were at play. I found the discussion of the 17th-century "reign of anarchy," the constitutional political culture, and the election of the kings to be especially illuminating, but really, the entire book is full of moments where I said, "wow, so THAT's what actually happened!"
In G-d's Playground, Davies is insufferably chauvinistic and gets bogged down in unnecessary detail; Zamoyski avoids all these mistakes and produces a readable, intelligent, and highly coherent survey.
The only caveats are more subtle, and based more on what is not said than what is said. Zamoyski is a Polish patriot hidden in the historian's objective cloak; he almost entirely neglects the competing interests of the various people once subsumed under the Polish-Lithuanian Commonwealth: Hungarians, Bohemians, Lithuanians, Latvians, Byelorussians, Ukrainians. One needs to look elsewhere to understand the interests of these peoples. I can't really fault Zamoyski for this, since the book would have been too unwieldy otherwise. But it's true, these other peoples appear mostly as stick figures in Poland's "empire."
The other problem is that he devotes only scattered paragraphs to the long Jewish presence in Poland. These are extremely well-written paragraphs, but nevertheless something is lacking. Zamoyski is so dispassionate, it is hard to tell if he thinks that anti-Semitism was a crime or even unjust (and I mean in the several centuries preceding the Holocaust). Regarding the Holocaust, he seems much more concerned with the damage it did to Poland's image, rather than exploring the roots of the terrible tragedy, surely one of the most momentous and horrible things to ever happen on Polish soil. He doesn't even make obvious gestures such as condemning the Home Army's stupidity in simultaneously rejecting Nazi ideology yet denying Jews the chance to enter its ranks.
Nevertheless, these caveats do not detract from a really superb book. As a Jew of partially Polish ancestry, I had always wondered what the larger context was, why the Jews settled in Poland and what was going on in that country outside of Jewish life. Most Jewish sources concentrate solely on either anti-Semitism or religious movements, and I found it so satisfying to understand the political, legal, and economic context. It really filled a gap in my knowledge and I'm grateful that I read the book.