I ran across this document, kinda lengthy, about what was thought to make a good game. It's a quarter of a century old now, but though it would be interesting to those here who are involved in game design:

http://www.atarimuseum.com/ARCHIVES/pdf/misc/design_of-IF.pdf
In fact there's alot of other interesting docs here: http://www.atarimuseum.com/otherprojects/lalab.html
Since it was written way before all the mainstream type interactive games seen today, maybe it could give you ideas on new angles on game design?