As a method, GTD is damn obvious to follow: Write things down so you don't need to keep thinking that you need to remember something, which would just lead into a constant need of keeping parts of your brain working on remembering instead of producing stuff; focus on what you should do next to complete said things you wrote down; and so on.
Part of the whole I was already following, so learning a few more tricks was really welcomed.
The problem here is the telling itself.
There are references to PDAs, like it was something not so common. Right now, almost everyone has a PDA in their pocket, although we call them "smartphones" instead of PDAs; there are references to "common" binders and rolodexes and that kind of furniture that, in today's world, is a pretty rare thing and most of the stuff we deal each day is digital.
There are some topics which are largely just propaganda for the method itself instead of going straight into it to give people an general idea of how things work and then going deeper (he does it later, but the very start is boring as hell).
Also, some final topics are mostly "One of my clients said she couldn't understand how she lived till this day doing things not GTD" or "I do this 'cause I like it", which although good to know, it's not representative of the method itself.
So while GTD is a pretty damn good method to keep things organized, the book that describes this is not well written, IMHO.
Get it for the methodology, and be ready to skip a lot of useless stuff.