9. Every Half-Life 2 Character Has A Real Person's Face

Half-Life 2: Raising The Bar is an invaluable source for trivia on everyone's favourite Valve game (because, funnily enough, bonus fact: Half-Life is the only original game they've ever made, with ever other Valve title being a derivative thereof, a sequel to something else, or a fan mod made official using the Source engine). Along with a bunch of development notes and sweet concept art, the book is packed with weird facts and behind-the-scenes snippets you'd otherwise never know about. Like how every single person you come across in the game is modelled off of an actual person's face. The immersion in the original Half-Life is pretty great, what with the lack of cut scenes or level breaks, but the one place it falls down is the NPCs. Every single scientists has the same face, as does every security guard, and they've all got the same voices to boot. Half-Life 2 got around that problem by "casting" people as the various characters you'd come across during your adventures, drawing mostly from Valve's own development team and employees and even, in the case of Doctor Eli Vance, a homeless man that they found on the street and (presumably) rewarded handsomely for being the face of one of the most important characters in the game.