Densely packed with a lot of really complex ideas, yet written in a manner that makes that information accessible and non-threatening.  The illustrations a cartoonish, in the style common to the rest of this series, and they offer support for the text, which is itself very readable and clear.  It is guilty of one of my major pet peeves — a “timeline” on the initial end pages that fails to represent the passage of time properly, spacing all the dates equally, regardless of the amount of time between them — but given the quality of the rest of the book, I’m willing to forgive this fault.