At first I thought it must just be another no electricity/post apocalyptic spin...but the characters are using swords and crossbows. Why would people move away from firearms unless they *had* to? Not that the Emberverse explanation for gunpowder no longer working makes any sense...but at least there is an attempt at a reason behind everyone wielding medieval weaponry. It's not like 15 years would be so long that Americans could run out of firearms or ammunition, ammunition doesn't expire, and an EMP wouldn't affect ballistics at all.
SA confirms that it is based on the Emberverse books, but it still is a mystery to me why the relationship is buried so deep and not being openly referenced. Does Kripke not want people reading the books and being turned off by them or reading about the supernatural aspects? I don't know much of anything about Stirling, but it seems like most any writer would want the publicity associated with a major network show. eta: I'm also a little sad at losing the local focus on the Willamette Valley. I gotta admit that one of the reasons I kept reading was the setting of the first few books in and around MAH LAND. Which is remarkably temperate and fertile, IJS.