Ever enjoyed the craftsmanship of a hand-made product? The effort of sourcing the right materials and putting the hours of work in perfecting just one unit is simply valuable to the beholder. Every detail gives its value and it speaks volume of the craftsmen who made it.
In games development, usually no one can solely build a commercial game alone without involving others. But it is important to recognise there is someone that leads the project, perhaps a collective agreement. An agreement that determines what the game would turn out to be; be it the experience of play or the intricacies of the game.
Given that games are essentially "hand-made" (until if ever artificial intelligence takes over the world), there is a certain amount of value that can be augmented and that is the aesthetic design of a game.
Some regards the aesthetics as the experiences of play, but the player's experiences is actually the by-product of the design. If we look abstractly at its meaning in games design context, we could summarise it as a judgement of something in harmony.
When defining a design goal, you have to first understand the relationship between game mechanics and each individual content of a game. Both of which play the role of setting up the experiences of play. Once that relationship is grasped, you can easily visualise how the game will turn out to be. With it you define the game's design goal. What are its pacing? Do your words contradict each other or plays together nicely? Are you being sensible of your capabilities?
In conjunction, a more humanistic approach can also be used to define design goals such as an experience you went through in life; be it a road trip with friends or your first encounter with a cockroach.
In your best way possible, define it in a sentence like a well prepared pitch to an investor. This can help you scope and sculpt your design goal.
Game mechanics and its content are to work together and be consistent with the design goal no matter its technological capabilities. This will lead to a respected and appreciative response from the player.