I read game manuals and strategy guides like my dad read the newspaper while eating breakfast on summer mornings. They had so much little bits of world building in the writing and design. Reading manuals on the ride home from the store set the tone before you even fired up the game for the first time

Games like Metal Gear Solid had mini comic book sections with loads of awesome artwork for their manuals

Manuals and guides are responsible for making me a gun nerd! Looking at the history and use cases for each one in the game carried over to the real deal. I remember guides for Rainbow Six, Medal of Honor: Frontline and Syphon Filter 2 being full of stuff like that