The structure of a game sets the stage.
The semantics of a game sets the atmosphere.
The abilities of players and characters dictate the kind of stories that can be told in-game.
Too few abilities stifles expression. Too many abilities stifles creativity.
Too few semantics stifles expression. Too many semantics stifles creativity.
Too much structure stifles expression. Too little structure stifles creativity.
I wish I could recall the fervor of the ideas with which I began this post. Perhaps too much structure.
These are all various angles one may hold a game. In order to examine it. In order to evaluate it. Play is the emergent behavior of an intelligence in contact with a healthy balance between the three.