Okay, you can now officially ignore the last four essays. I was using very muddy terminology. Here's the new explanation:
Every game (and every other kind of art) is designed based on some fundamental bits. These are not the things the player gets to see or interact with, at least, not directly. These are the foundation for those things. These are the things which anchor play, anchor plot, anchor the art.
A lot of people play a game and like it or dislike it. Then they attempt to justify this like or dislike: "It has a great story!" "The gameplay is innovative and interesting!"
The thing is, a huge number of games have a great story, or great gameplay, or great art. But those games are never really mentioned. If a great story, or great gameplay, or great art were the real requirements, those games would be very popular.
You can argue that a game needs all three things combined to be very good. That's not entirely true, of course: some really fantastic games are missing one or even two of those things.
Justifications never work out very well. The real reason most people like or dislike a game (aside from hype and/or critical software issues) is dependent on the game having deep, cohesive, and fully utilized fundamentals.
Most genres come with some fundamentals. RPGs come with a few story fundamentals: save the world, gather a group of random people, explore the world. They also come with some play fundamentals and even some art fundamentals. Most RPGs simply use these fundamentals and produce an average product.
Some RPGs toss in some new fundamentals, creating a crazy-quilt of ideas that mesh poorly. Some people will like these RPGs for their innovation, but most people will find them unappealing.
The best RPGs put in new fundamentals that cut across the way the player experiences the entire game. These fundamentals allow the content of the game - rules, art, story - to unify and resonate. They allow the game to shine, because they create pearls and then shine lights on them.
These fundamentals don't have to be complex. For example, FFVI's two cross-cutting fundamentals were "emotion" and "lots of characters". Not exactly complex. At least, not on the surface. But these two fundamentals allow the rest of the game to be built beautifully.