If you look around in Portal, you can see the graffiti from previous "test subjects" warning you not to trust GLaDOS. While Portal's treatment of environmental storytelling is pretty simple, the upcoming game Gone Home takes these aspects of narrative design and zeros in on it. The first-person exploration game by the Fullbright Company lets players explore a family home from 1995.
Do you remember the 90s? When a cordless phone was the hot new technology and Sailor Moon was all the rage? My parents had a big collection of movies they'd taped, and I made an alphabetized list of them as a chore. Little details like these occur in the game, evoking that time period in a way that doesn't just reference videogames from the era. Eurogamer's Jeffrey Matulef describes a few of them.
A crumpled up note in Sam's waste bin [...] turns out to be a disciplinary note to her friend who was reprimanded for wearing a Pabst Blue Ribbon sweatshirt to school. A health class homework assignment on menstruation has the date, and teacher's name in the corner, while a mass produced letter from the new principal addresses the community in that bland, professional manner that ensures no one will more than skim it thinking "yeah, new principal, whatever." Even the mom's note from her old college friend Carol is written on the kind of floral stationery that everyone's mom had back then, and it's scrawled in that very particular penmanship specific to women who grew up in the 1950s.
While the game's audio diaries may make some explorers wince at the impurity of non-environmental information, they can be turned off for a more contextless exploration experience.