As an Industrial designer I've read many design books related to my profession, there are many that cover specific subjets of the practice but there are some that I think could be of great value to game designers.
Recently I've been re-reading John Maeda's The Laws of simplicity (http://lawsofsimplicity.com/), which I think is a great book for board game designers as it treats simplicity as a concept not neccesarly applied to product design.
Maeda breaks simplicity into ten laws (and then three keys) that can be applied to make things simpler.
Another book I can see of interest is Donald Norman's Emotional Design (https://www.jnd.org/books.html#emotional-design). Norman is a reasearcher on cognitive psychology and has worked with many Universities and some of the biggest design firms.
Emotional Design is all about how emotion inform how we percieve and interact with objects and what are the mental processes behind that. Norman writing is very accessible and engaging. It even has a chapter about fun and games of which I remember absolutely nothing except that it exists.
Laws of simplicity is highly recommendable to those designers struggling with complexity in their games. If you go to the book website there is a brief summary of each law.
