My opinion is that the game is its mechanism. Any discussion around this point is just an exercise in theory. When you have a working mechanism you have a game, and when this mechanism is enjoyable, you probably have a good game.
Quotes by Daniele Tascini
[…] most of the time people who like this kind of experience simply love the theme so much that they will sacrifice cleanliness, elegance, and game length to privilege the simulation of reality.
I believe that starting a game from the theme is impossible and untrue. When you say, “I’ll make a game based on Star Wars,” you’ve said absolutely nothing. All you’re doing is procrastinating the process of thinking about the mechanism.
The reality is that a mechanism without a theme is still a game, but a theme without a mechanism is just a theme.