New suggestions on the theme 'SUBSTANCE AND DESIGN':

Within both categories there are special qualities they have to fulfill.
The 'interface' is within the 'responsibility' of both.
Both together in connection to each other are responsible for the game 'being intuitive'...

Within 'substance' there are 'reliability', 'easiness of the controls', 'lucidity'(Übersichtlichkeit), 'fairness'(relating the AI and the information it bases on)...(to be continued)

Within 'design' there are 'identification', 'touch', such as the 'connection' to the gamer, the player's heard, experiences, emotions, knowledge, to the player's world and thus to the expectations which this world makes probable.

Let's talk about 'connection': the design has to connect the elements which the substance provides in the head and heart of the player. It has to take care that the player doesn't loose the thread! The thread/connection between the elements, the meaning of their relations, but also the connection between the players motivation to start the game and reasons to continue playing, the connection between head and heart: means the mind puzzles and that they actually evokes feelings. Even the math puzzles are rewarding with pleasure about a solution with the 'cleanness' or 'simplicity' and that it rewards with the 'shelter' of being 'enclosed' and 'rounded', escaped from threatening chaos and problems.
'Design' not only provides the player with pleasure, desire, disappointments of getting/missing rewards, but rewards the player 'while' playing with nice sound, nice ambient, gimmicks etc..
And here we go and come to the main idea that struck me today:

The design provides a 'while' (while playing), it provides the player with celebrating each moment, it organizes the playing as an event.
That's
'production/staging' (in the sense a play is presented in a theatre) ("Inszenierung")

Remember other games beyond pc and consoles to realize what I mean:
for instance 'soccer': when they express their pain when fowled, their pleasure when they shot the goal, how they prompt the fans in the audience to support them, how they show their anger etc. - all this sort of communication between the soccer team and their fans.