Solidly ok. I really enjoyed Chapter 7 on how to review your prep, and Chapter 10 on creating and using templates for your scenes. For the value of those two chapters, I felt it was probably worth the price and worth my time spent reading the whole thing.
Much of the rest read like painfully dry time-management self-help. Maybe that's something other GMs need, but I don't need to be reminded of how few hours in the day I really have or how to shift my other tasks around to make room for game prep. I definitely, definitely don't need special little names for each type of life's normal interruptions. I'm an adult and have been juggling various combinations of marriage/school/work/kid/hobbies for a while. If I wanted a self-help time-management book I'm not sure I'd come here for it. But maybe this would help someone who is just getting started with trying to strike a balance in life.
I strongly suspect this guide would be more helpful for someone running a campaign. At present and for the foreseeable future I run published one-shots or short modules. I want to be better prepared for those, and as a newish GM, I hoped that this guide would help me. But I don't really need to brainstorm, somebody else wrote the material for me.
I do appreciate that the PDF was well bookmarked, so that if I do find myself wanting a refresher on brainstorming, conceptualization, and documentation, I might come back to this guide. If I can talk my new group into committing to a campaign one day, I'll probably be more glad I read this.
[3 of 5 Stars!]