Well, here's another one of those opportunities in gaming culture to date yourself. Doom, better known as "The FPS that defined the FPS as we know it today," has now reached the crusty old age of 20. Keep in mind that this was not the first of the first person shooters, there were predecessors, including iD's own Castle Wolfenstein 3D. But Doom has the distinction of being--like Halo after it--the game that reached out to the masses and made them aware of the genre in a big way. Doom got its start in a way that no self-respecting developer--including iD itself these days--would dream of doing. They made the game, uploaded the first of its three "episodes" to a software BBS and an FTP server at the University of Wisconsin, and then asked people to download it for free and pay if they wanted the full, "registered version," while spreading the word about the game. It's a concept called "Shareware," which is almost entirely dead now, but it got Doom installed on over 10 million computers back in the day, and clogged so many networks with multiplayer matches that universities--and even companies like Microsoft--had to start regulating when people in the office could play the game.
Today, Doom is more of a historical footnote in games, like Metropolis is in cinema; it's something that almost everyone has heard of, but enough time has passed that not everyone has experienced it. The latest installment of the series didn't make the same waves as its predecessors, and even its creators, like John Carmack and John Romero have moved out out of the sphere of big budget, AAA games. Romero has been creating apps, while Carmack recently resigned from iD as one of its executives and co-founders to focus on Oculus Rift. Regardless of whether these industry giants have moved on, and the FPS du jour is now Call of Duty, every time you play a game where you wander around in corridors and see your own gun floating in front of you, or you play some multiplayer with a mode called "Deathmatch," that's all because of Doom. So happy birthday, Doom. 20 years as a game franchise that people still recognize is a serious accomplishment.