AAAAAHHHHH!!!!! What a book!

It's the one that won Hesse the Nobel Prize for Literature. Yeah, it's a lifetime award, but I gather it's generally awarded after a particular book comes out that makes everybody say, "Wow!! S/he's been great all along, and occasionally better than great. But this is amazing!!!"
Magister Ludi means
Master of the Game. As Av said, the game attempts to reduce all things to symbols. But it's more than that. A string of symbols might mean 6+7=13, do-fa-re-ti-do,
How do I love thee..., the Grand Canyon, and any number of other things - all at once. Depends on which discipline you're interpreting the symbols in. In the Game, you start with whatever, let's say do-fa-re-ti-do, and write it in the Game's symbols. In the next step, maybe you reinterpret those symbols as math, and you change things as you go.
Now don't get the idea that you're going to actually learn about how to play the game. You don't. The book is more about how the Game gives the players their particular philosophical outlook, and how that outlook compares to those of the other people Joseph runs into throughout his life.
I could never say enough about the book. If I read as fast as you do, duchess, I'd reread it every few years. But I'm slooooooooow. (Took me 6 days to read FR, to give you an idea.) It's not light reading, but you will go through it much easier than me.