The A-G Piano Book Series takes a pretty different path then most piano method books.
From a teaching perspective, it is written with the intention of decluttering music education. Every teacher has their own way of doing things and every student requires a unique approach to teaching. This book aims to provide educational materials and fun songs for students to play and learn from.  
The music has been written to be educational, but be rooted in contemporary aesthetics. Less classical, more like movie and video game music.
This book is designed within a principal of minimalism. There are no teacher duet parts or long explanations of concepts.
This music is designed to be more accessible to students who learn by ear and by pattern-recognition. When I was a piano student I always struggled with reading, but excelled at pieces where I could identify chord structures or patterns and then could just memorize it. I believe I’m not alone in this and a lot of other students are like this. This book is for them. 
Learning to read music is also important, and this book series stresses a ‘skips and steps’ way of doing things, as opposed to hand positions. I believe this encourages flexibility in reading at an earlier stage
In relation to a lot of other method books, the right hand has more shifting, and more difficult fingerings, but the left hand is much simpler.  Fingering is often left up to interpretation deeper into the series. This book does very little hand holding. The whole series is structured a little bit like a video game. It gets a lot of the tutorials out of the way early on, and then focuses on teaching through experiential learning.