To paraphrase what Rothfuss says himself in the foreword - you might not want to read this book. If you haven't read his two main works The Name of the Wind and The Wise Man's Fear it will make next to no sense and even slightly spoil them.
The Slow Regard of Silent Things is a very odd book. Main character Auri as we (slightly) know from the two main books set in Temerant lives in the darkness and the quiet beneath the university. She walks in rooms and halls long forgotten and abandoned. She finds the right names and places. She knows which day is a good day for making soap.
This book is madness. It spans less than a week. Barely anything happens really. But yet so intensely much does. This book is fantastic. I loved it. I love it still. Rothfuss is an ingenious man and his writing is superb and I'd love to read several more books like this in between his main ones.
Be warned that it is a very different sort of book. Be warned that it might enthrall you entirely.