The AOE games provide replayability through randomly generated worlds, variety of maps, variety of game types, and multiple civilizations to be played. A great game story keeps the player engaged, intrigued and playing, increasing satisfaction. A great story uses plot twists, reversal of fortune, and other ploys to keep the player interested. Adventure games require the designer write the story and the player act it out. RTS games usually provide no story, but instead an empty map, like an empty page, on which the players write the story themselves as they play.
Game development is more an art than a science, and therefore difficult to predict.
Developers must demonstrate that a project is making good progress toward a goal. Publishers must assess that progress. There is no reasonable justification for major compromises in the quality of a product. Make a great game or kill it early. One of the values of early prototyping is that it can reveal that a game is not going to work early in the process.