The core works are readings which you can use to learn in depth about game design:

• Dave Gray, Sunni Brown, and James Macanufo. (2010). Gamestorming: A Playbook for Innovators, Rulebreakers, and Changemakers (1st. ed.). O’Reilly Media, Inc.

• Fullerton, Tracy. (2008). Game Design Workshop. A Playcentric Approach to Creating Innovative Games. 10.1201/b22309. 

• Jesse Schell. (2015). The art of game design: a book of lenses. Morgan Kaufmann Publishers Inc., San Francisco, CA, USA.

• Staffan Bjork and Jussi Holopainen. (2004.) Patterns in Game Design (Game Development Series). Charles River Media, Inc., USA.

• Mary Flanagan and Helen Nissenbaum. (2014). Values at Play in Digital Games. The MIT Press.

• Alexander Zook and Mark Riedl (2013): Game Conceptualization and Development Processes in the Global Game Jam-text, Georgia Institute of Technology. Atlanta, Georgia, USA

• Brenda Brathwaite and Ian Schreiber. (2008). Challenges for Game Designers (1st. ed.). Charles River Media, Inc., USA.