I teach 5th Grade history, I mean "social studies", and let me tell you, as a teacher, I'm always on the hunt for material that will engage my students (and myself). The Horrible Histories series, and "The Angry Aztecs" in particular, are a godsend. My students and I love the information in the book and the humorous way it's presented (the illustrations are great, too).
I've read other books in the series, and the author shines the same light on the unfortunate aspects of every culture he presents (see "The Measly Middle Ages" for a great take on Europe). If nothing else, you will be grateful to be living in the USA in this day and age when you're through with the book.
Human beings have been (and continue to be) horrible to each other, but if we can learn how to move away from superstition and learn from history's mistakes, we'll be better off. These books will help in this endeavor.