"Lies" is about the outright lies, omissions, and boringness of US history textbooks. The book was filled to the brim with interesting historical facts mixed with a dash of outrage at the system.
Loewen loves history. That's why he's sad that history is the most hated subject in school. He blames this, largely, on history textbooks. These textbooks aren't just biased (though they are biased); rather, they take out everything interesting, including all of the controversy, all of the ideas, and anything that makes anyone seem bad.
In each chapter, he goes over what all of the major history textbooks do cover, he talks about how that is a horrible way to cover the subjects, and he tells some of the interesting stories that they should be telling. He also shows how this is hurting students.
For instance, in the section on European colonization of America, Loewen addresses the myth that the US government bought land from American Indians, and the Indians didn't understand the terms of the contracts because they had a non-western understanding of property rights and land use. In fact, they often did understand the terms of the contracts and western conceptions of land use. As a result, a lot of the contracts that they made were basically leases -- Europeans could farm the land and travel across it, but they couldn't develop it or prevent Indians from doing anything. Thus, of course, the Europeans later violated these sophisticated contracts. In other instances, Europeans paid the wrong tribe. For instance, when buying Manhattan, they Europeans paid an enemy of the tribe that owned Manhattan for Manhattan. In other cases, Indians weren't even involved. For instance, France never really bought the land that they sold to the US in the Louisiana Purchase. They just had a "claim" to it.
The whole book is filled with stuff like that, from presidents, to socioeconomic status, to slavery, to the civil war, to reconstruction, to the civil rights movement, to Vietnam, to more recent history.
I highly recommend "Lies My Teacher Told Me" for anyone who is interested in history. I also highly recommend it to anyone who was turned off of history because the subject was dull. Loewen does the subject justice.