At first, I thought the spellbooks were great. Then I went through a short phase of finding them kinda clunky and slow. Now I'm back to thinking they're great again and I think my mindset will stay that way.
In short, the organization the books provide speeds up play for me. They let me look at 4 spells per page (or 8, if you use their fronts and backs), which was daunting at first, but after you familiarize yourself with your book and get a general feel for the spell-types, it becomes more efficient. I also like the feeling of knowing exactly where to turn to in my book to deal with a particular situation.
I guess how I feel about the book style came in 3 phases; exploration, as I learned the game; a kind of "study" period where I tried to digest all the different spell-types; finally, I feel like I "get" the intended feel of the book, the purpose of which is to let you feel like a mage.