I have books 1 - 5 of this series and it looks like it would be really good for someone interested in being able to play more popular styles.
Christopher Norton is the primary author and Scott McBride Smith also contributed. From what I've seen online, Jon Michael Iverson did some of the videos on the website.
Here is the APP website: http://www.nvmusicgroup.com/NVWeb/Home.html
There are a lot of ensemble pieces in the Repertoire books and the Etude books are mostly about improvisation. For example, the level 5 Repertoire book has 8 lyrical pieces (which focus on melody, legato, etc.), 8 rhythmic pieces (which focus on popular rhythm styles), and 8 ensemble pieces (which focus on ensemble and duet playing). The cd included in the Repertoire book includes two backing tracks for each of the ensemble pieces (at a practice and performance tempo) and backing tracks for the improv examples in the Etude book. The level 5 Etude book has 8 improvisation modules based on pieces in the Repertoire book, with 4 modules for each improv piece. It then has a fifth example of these pieces, part written out and part to be improvised as a performance etude. Finally, 8 classical pieces/etudes and 8 additional etudes by the authors finish up the Etude book.
From what I can see, this series starts at beginning level and progresses pretty well. I am waiting to be able to get levels 6 & 7, as from what I have seen this corresponds to the level 4 Keith Snell books I am working through.
These books would work fine for an adult student under the guidance of a teacher. There is little to no direction for technical skills in the books I have. (This may be included in the Technique and Skills books, which I do not have.) There are no pictures on the pages; however, the pieces have titles that are suggest that it was written with children in mind. If you are looking for familiar tunes, this is not the series for you. To get the most out of the book, you want someone to play the ensemble pieces with; however, the backing tracks on the included CD would help.
An alternate series that would provide similar material is Christopher Norton's Connectionshttp://www.christophernortonconnections.com/index.html