This may be kind of stream-of-consciousness, but I was thinking about how RPGs (especially Japanese console RPGs) are structured.
First, there’s the tutorial area. This area is designed to give the player a chance to get used to the game mechanics. The player usually isn’t in a lot of danger in this area, and typically can’t leave until they’ve accomplished the quests in this area (and the quests are designed to “prove” to the game that the player understands the basic mechanics).
Then the player leaves the tutorial area. Typically, this is when the player encounters the game’s villain for the first time. This is done so that the player can understand the nature of the threat he is up against. Sometimes the player will be forced to fight the villain, and will lose. If this happens, the villain won’t kill the player. Better games find better ways to demonstrate the villain’s power level without putting the player into direct conflict with the villain at this time (Final Fantasy VII’s flashback where the player plays alongside Sephiroth comes to mind).
Once the initial confrontation with the villain is over, the Journey begins. The player cannot go directly to the final confrontation with the villain, typically because the villain does not even exist in the gamespace at this point. Instead, the player travels from area to area in the game world. In each area the player meets new and different people with new and different problems, problems that have typically been caused by the villain. Thus, the player sees the villain’s malice firsthand and tries to undo as much of it as he can. He is rewarded for this with an increase in his power level. The game usually forces the player to explore every area of the game world before allowing him to proceed to the final confrontation with the villain.
In order to defeat the final villain, the player usually needs two things: a “key” object that either allows the player to get to the villain or makes the villain vulnerable, and an appropriate power level so that the player can survive the actual battle. Once the player defeats the villain the game is over, though some games allow the player to continue to play and see how his actions have affected the game world.
That, in a nutshell, is how an RPG’s gameplay is typically structured.