Here, I'll start. When I was 8 years old, my parents went to a dinner party and plonked me down in front of the host's computer so I'd stay out of their way. The game they booted up to keep me occupied was Space Quest II. Little did they know what impact that would have on me...
That's going back a ways... I think the first one for me was King's Quest 1, actually. "KILL SNAKE WITH SWORD" was far beyond what I could type in the amount of time I had to type it, but the idea of moving around a screen interacting with the world to solve problems was utterly intoxicating.
The second one was Leisure Suit Larry, which I probably should not have been allowed to play but I was the only one who knew that at the time. Perhaps fortunately I never got very far in it, but the boss key made me laugh hard enough to make it worth it.
It wasn't until somewhat later that I encountered the Space Quest series, which I really got into. I actually completed some of them!