Narrative - Designing Games - page 100

For some games, a simple structure like this is enough. Often, though,
we need to combine story-ordering devices in a more nuanced way to fit
the needs of the game.
Mega Man 2 : The game starts in a hub and spokes model, since the
player may defeat the eight robot masters in any order. Once they're all
defeated, the game switches into a linear sequence as Mega Man assaults
Dr. Wily's techno-castle and moves toward the game's conclusion.
Mass Effect 2 : The start and end of the game are linear strings of
pearls, while the middle 80% is a giant pile of quests softly ordered by
player skill and character level, with a central quest running through the
middle using branching and story convergence. This hybrid structure is
popular because it combines so many advantages. The designers get to
script a careful introduction which introduces the story and game me-
chanics. During the softly ordered central portion, the player feels free
and unconstrained. Finally, the game's climax can be carefully authored
for maximum effect.