David Brevik, one of the original developers of Diablo has released the original pitch document. Check it out!

Anatomy of Diablo’s pitch document

• Summary
• Game Design
  • Overview
  • Plot and Setting
  • Gameplay
• Marketing
• Development

In addition to illuminating how to write these documents in general, I find interesting to see how the Diablo devs were planning on leveraging the success of Magic: The Gathering’s business model to sell DLC.