For me it was Grand Theft Auto, released 1997. Fun times.
I reinstalled it using Wine last year. It ran well (only the cheat codes didn't work), but it didn't really transport me back to my youth the way I expected it to (I played it a lot at the time, so thought it might the way other games from my childhood, like King's Quest VI, do) and I grew bored of it after a day or two.
GTA III was the first one I played for more than 5 minutes! The last one being San Andreas.