Yes, the original Getting Things Done book is thorough and excellent, and the next one, Ready for Anything, is great as it helps ease you into the ideas behind it. But Irondavy is right, when you’re really ready, read GTD.
Personally, yes, it’s absolutely as good as people say. I actually did organizing coaching for people even before I read GTD, and after I read it, I started coaching from within that framework. It’s that good. It’s comprehensive, without being dogmatic. It’s a set of principles. There’s really nothing to rebel against. How do you rebel against gravity?
If you don’t have a trusted system, stuff goes back into your head for your mind to manage it. If you’re ok with that, fine, but please realize that it will have a cost on your attention, your energy, your productivity, your creativity, and your ability to enjoy your life. If you’re interested in having all that, develop a system that you trust and manage regularly. That way you get a free head.