'Progressive 'systems are systems in which the user completes sequential actions in order to reach a definite end (Bogost 121). A linear game such as Halo may be considered progressive.
Progressive games are more likely to be associated with coherent worlds and the adventure genre, and as such their storylines are usually linear.
In Half Real: Video Games between Real Rules and Fictional Worlds, Jesper Juul differentiates progressive games from emergent games, which provide a set of rules which produce unpredictable consequences, and are inherently non-linear.