Mistborn: Secret History

The Mistborn trilogy, and the following Wax & Wayne series, are one of the most elaborate and interesting magic worlds I've ever read about. As a hardcore fan of the world, Secret History shows an alternate take from the end of Book 1 up until the end of Book 3. I appreciate that Sanderson had a bit more in mind than we were able to see in those books, but I didn't feel like this added as much to the world as I was hoping for.