I would say the original GT (and especially GT2) changed my life.
I always had a love of cars, but got much more interested in them because of those two games. If it weren't for those two, if I had never played them especially, I wouldn't have had the desire to try switching from my old job to being a mechanic 10+ years ago.
GT4 didn't really change my life, instead, its vast library of cars gave me more enthusiasm about them. Back when I was into GT4 (2007-2010 ish) it was often possible for me to drive a car at my job, and then drive the
same car in the same day, but this time in the game. Camaro, Mustang, VW Golfs and Beetles, Miata, Toyota MR2, Mitsubishi Galant, Lancers (including at least one Evo), Subaru Impreza (including WRX versions, though no STI dammit), Jaguar X and S-types, Civics, Accords, Infiniti G-class, Lexus IS and GS, Mercedes C and E classes, Mazda Protege, Eagle Talon, Dodge Rams, (etc.) the list goes on and on. We even have an NSX which occasionally shows up!