At the outset, the way in which video games typically use the word “genre” seems at odds with its more conventional literary and cinematic usage. However, arguably, by emphasizing a means of delivery, video game genre becomes the format informing emotion, which is not so far from the word’s more thematic meaning at all.
Just as the tropes of film genres train audiences to anticipate certain modes of behavior (we generally expect the action hero to kill to get what he wants, just as we hope that the romantic comedy lead doesn’t), video game genres emphasize the power dynamic between players and events. Players, in turn, develop distinct emotional ranges and expectations within a given genre, and these are continually modified and projected by a game’s content. You expect to exert a greater level of tactile immersion with the full sensory space in a first person shooter than you would a 2-D platformer, so a game like BioShock brings about its emotional reaction in part by violating that very expectation of (albeit illusory) player-character autonomy. Following on that idea, the comparatively high compression of a 2-D platformer’s player-space interaction means that the player’s main dialogue occurs first and foremost with the space’s physical laws, rather than with its social ones. In this way, platformers’ interests tend to fall thematically within two familiar conflicts: man versus nature and man versus himself.
Thus, in one sense, video game genres are more liberating than many others because they allow any number of thematic elements within the same conversational framework. You can have first-person shooter romantic comedies and political thrillers that are also visual novels, and these are acceptable in either case.