Now, while every entry in the Final Fantasy series has its own plot, characters, settings, and such, there are various elements that occur throughout.
For starters, the protagonist is usually missing some memories, which will end up being key to the plot. He/she is more often than not involved in a struggle against an evil empire, corporation, or malignant military power, which is at the forefront for the first part of the quest.
But at some point, usually about a third of the way in, the villain is introduced. The villain often tosses what was previously the main conflict right out the window, and begins antagonizing the hero and his/her band of characters. After some initial skirmishes, the villain will typically end up getting some massive boost in power, and go off to wait somewhere for the hero to come a'lookin'.
It is at this point that the player obtains his/her own airship, and can travel around to anywhere in the world they like, completing side quests and getting more powerful. When the player is ready, the hero heads into the villain's lair for the final showdown, which commences after some long-winded speeches about life, love, or existence itself. At some point during the battle, the villain will almost inevitably shed their human form and become some sort of huge monster.
The hero wins, and on comes the lengthy end cutscene. Several times, the end cutscene has employed the old, "Holy cow... is the hero DEAD??!!" trick, but not always with the same outcome.
It remains to be seen whether Final Fantasy XII will continue these trends when it is released in the fall.