What distinguishes it from most popular entertainments is that it's about big ideas and big events in history, presented in a way that really gives you a sense of those events and ideas. "Quicksilver" covers the last half of the 17th Century in Europe, with particular attention paid to the beginnings of the scientific revolution. Isaac Newton, Leibniz, Samuel Pepys, Charles the II, Oliver Cromwell, Louis the 14th, Huygenes and many other historical figures mix into the story, and after a while it can seem to be a bit like literary starfucking -- "say, isn't that young Ben Franklin I see over there?"
But it's really remarkable the way Stephenson ties religion, politics, science, and commerce together -- in essence they're all interactive parts of the same chaotic whole. Since I'm a middlebrow I didn't really know much about this part of European history, and now I feel painlessly slightly better informed. And it is remarkable that banks, Calculus, the scientific method, and the modern concept of personal freedom were all invented more or less at the same time.
And the book is full of humor, both high and low. Sometimes Stephenson reaches a bit too far -- an aside about "Canal Rage" in Venice maybe puts too fine a point on. But I'd be pleased as effing punch to have written a book half this expansively good.