I am not sure how much of a departure this book is from books like Fierce Invalids Home From Hot Climates and Perfume the Story of a Murderer. Yes, those books relied a few facts in telling the story - like the way fragrances were bottled in old times and oddities like a clay lick for the birds - but those two stories were hardly what I would consider reality-based.
Charlie and the Chocolate Factory was fantasy. And Inamorata, while based on "real" facts, had an air of uncertain, quasi-fiction to it. Public Enemies was a recitation of pure facts....but even books like Shantaram, which was based on a true story, cautions us to consider it a work of fiction.
And like most of the books Johnny has guided us to, I think Glass Books was very well written. From the first paragraph, I was hooked. I didn't always like where the story took me, and sometimes I had trouble keeping all of the characters straight, but overall I thought the writing itself was superb. My mind was filled with mental pictures all the way through, both with regard to scenery and characters. I could see a virtual movie in my mind while I read! My copy has a lot of post it notes marking "favorite" passages. There were some great passages.
I think there are some really strong moral currents under the surface. Once or twice I saw something beyond what was written on the page and I thought "Oh! That's what Johnny saw!" That will be fun to explore as this discussion goes along.
So I guess my answer is that this was an interesting choice for ONBC and it was different but it wasn't out of place with the rest of the books we have read. Thank goodness there are many dimensions to Johnny Depp's interests.