Hi Rick,

One of the ways to organize your requirements is to first think of your video game as a system made of various components or functional areas.  Try to decompose the game software into distinct domains and then, if necessary, further decompose each domain into sub-domains.  Then capture requirements for each sub-domain.

There are many ways to decompose the capabilities of a system:

• functional areas
• user types (personas)
• baseline features (MVP) vs. add-on or advance features
• key processes (process model)
• data flow model
• etc.

Here are some additional helpful resources:

• Article: How about Organizing Requirements?
• Forum Thread:Structuring and Organizing Requirements Specification 
• Forum Thread: How to organize Features and Business Rules for further discussions? 

Hope this helps!

Adrian