The book was incredibly thorough in its scope, which was just what I was hoping for. While it's an invaluable resource for conlangers, it's also great as an overall introduction to linguistics, which is why I picked it up. The one linguistics class I took at university didn't go nearly as in depth as David Peterson has done here.
But also, I've been having trouble learning a second language for years, and I was convinced it was because I couldn't pin down the name and function of what I was learning, everything was so vague. If only I knew the technical terms and definitions for all these linguistic and grammar rules, really break it down into its most basic parts and look at each individually. This book was great for that.
Final thoughts: I was surprised by how quick of a read this was! Peterson made each topic both accessible and fun. I loved the part about sign language articulation. The sign language IPA was fascinating.