DooM. The game that defined my early-to-mid teen years. How old was I when this came out? 12. However I did not have Internet access, and was kind of cut off from most mainstream games. Played Wolfenstein shareware for Mac in December 1994. But voilà!!! somewhere in mid-1995 I got a CD with lots of shareware games ... including DooM.
The game had things that no other game had: while 3D FPS were already there, most of 'em were like the corny Area51 that were basically "your character moves, shoot, reload and pray they don't hit you". Wolf3d was good, but lacked a true 3d system as it was basically a series of rooms with always 100% lighting. Doom was Different. It had different levels, interiors AND exteriors, a sky, lifts, doors, switches, you call it. But most important: dynamic lighting. Or should I say, darkness??? First thing I found out with this game was that some lights flickered, some other lights turned off, like level 1-3 or some other nice traps. But level 1-5 "Phobos Lab", now that's DARK. I mean "I'm scared like hell" kind of Dark. This level was so spooky for me that most of my stuff kept being dubbed "Phobos Lab" for ages, even currently. (Cultural Note: Phobos means "fear").
Even though it may look like cheesy by today's standards, this game set standards back in its time, mocked by Duke Nukem, and well set the bar until Quake for graphics, and Half-Life for game-play. I proudly still own Ultimate Doom, Doom2 and some of the add-ons. BTW get Doom95 and you will be able to run DooM w/o resorting to DOS! :)