One of the things that caught my attention was that in the heavy use of the hoverboards throughout the story, it was never made clear whether Tally and Shey skated regular or goofy foot. I don't know if Scott Westerfield even thought of it. Maybe he's not a skateboarder. I imagined the main character, Tally as hoverboarding goofy foot (right foot foward) like myself while Shey hoverboarded regular footed (left foot forward) like my son.
Omitting this detail was perfect, if perhaps unintentional. Which way they hoverboarded didn't matter to the story and it allowed me as the reader to fill in the detail with my own imagination. In doing so, I more closely identified with the main character since I imagine her "skating" the way I do. Often less description is more. No two people will ever generate the exact same image in their heads so rather than try to describe everything in meticulous detail, allow the reader to get the most important elements and fill in the rest with their own minds, turning the book into a shared creative experience. The story is just as much the reader's as it is the author's.
When our book club read the Hunger Games by Suzanne Collins, one of the members of our club asked, "What does Katniss even look like?" I said it didn't matter. Until they made the movie out of the book and imprinted some young actress's face as the main character, we could imagine whatever we wanted. That is one of the joys from books, the reader gets to imagine the world and its inhabitants rather then be spoon fed the visuals like in film.