The final game is a fully graphical game. I had to decide what method to use to bring graphics into Lisp that would be the most valuable to learn. Since almost everyone can benefit from learning the nitty gritty of how the web works, I used the following steps:

   Step 1: Write REPL game
   Step 2: Write a web server from scratch using sockets
   Step 3: Write an SVG library
   Step 4: Implement an inline SVG-based HTML5 browser frontend for the game

If you're taking votes I'd love to see some OpenGL demos using something like the cl-opengl bindings.

I don't know the extent of your book, but navigating asset management has been a bit of a challenge. I know there's a few libraries out there but docs/examples are at a premium. I'm using cl-devil and looked at freeimage, also looking for 3d model importing and the like.