It's easy to have every idea you've ever wanted in a list. But good games aren't about how many ideas you had, they're about doing something effectively and sticking with it. The design goal may be graphics, physics, story, etc. A mission statement defines the game's goal in 1-3 sentences.

So what will the game's strengths be? What will it adamantly stick to and excel in? What features will be the most focused and dedicated? These may be obvious questions, but the purpose is to look at the foundation, the fundamentals of the design.

Too many times in the past, games have been dismantled due to the conflict between a dreaming designer and a realistic programmer. They emerge as a hodgepodge of features and half implemented ideas that don't equal a solid whole. Look at Daikatana (actually, don't).

There will be plenty of features that won't make it in to alpha or beta testing, or retail release. Ask yourself what features are most important for retail. Look at all ideas and features and put them in a category:

1. Primary design goal, will be in retail 2. Other goals, will probably be in retail 3. Additional features, should be in retail 4. Future features, possibly after retail 5. Uncertain features, might be implemented 6. Pipe dreams, wishes, and near impossible ideas