While this is a seminal work, I definitely wouldn't approach this like I would approach a textbook: it's definitely not meant to be friendly introductory material. That said, once you have a bit of background, it's a goldmine of a survey. You'll notice that each section is a short, few-page long introduction, but the bulk of the material is in the papers themselves, which can be significantly tougher to read. Though it's great that the summaries are friendly and help you contextualize the papers. My tip is to read papers starting with the introduction, and then the conclusion, and then decide if you want to dive into the rest of the paper to track down the evidence for specific claims.