I am creating this topic, because I haven't seen another similar one on this forum, and I'm interested in what games affected some people, and maybe even what age/point in their lives it happened..
The game which has had the biggest affect on my life would have to be Thief: The Dark Project, released in 1998, if I remember.. I was in college and had just put together a sweet system, with huge surround sound speakers, 21" monitor, a first-generation IR mouse (still have it!) And the first game I bought was Thief..
I played the game, and it was hard, and engrossing, and had wonderful AI.. I would get an increased heartbeat every time I slipped up and a guard would stop and say "What was that noise? .... Oh nothing, must have been a rat.."
The second level on that game scared me so bad, I had to stop playing for 3 days before I could sit down at it without getting shaky as soon as I opened up my savegame.
It changed the entire way I played games, once the "Lytha-style" playing term was coined, where you finished every mission on the highest difficulty without dealing any damage and collecting every item, and the seemingly limitless ways to finish every mission were truly staggering (and I still play as many games as possible this style, and drop the game if you can't..) Years later, IRL, I still tend to avoid loud surfaces, and I tend to move toward shadowed areas.. I read the "1000 reasons You've Been Playing Too Much Thief," and most of the 1000 points given, still apply to me even to this day..