Reddit mentions of Inside Game Design

Johan Huizinga's work is pretty foundational to the philosophical underpinnings of games.

Man, Play, and Games is another significant work that predates video gaming.

On a less academic level, Inside Game Design is a book of interviews with several studios of varying success on the game design process and how it adapts from game to game.

These titles might be pretty fringe to what you're looking for, but I can recommend some web pages that provide more easily digested, general interest material that would be helpful to you. I also know of a number of relevant academic journals, if that is of interest to you.