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...
Holy crap, you sent me down a rabbit hole and a trip down memory lane. I remembered the cover of the first CD game I ever played but couldnt come up with the name, so I just read through all Point n Click adventures wikipedia knows off, looking for a bright green background and a weird clown on top of it.
It was Toonstruck! Never finished it, but it was my first PnC, so I guess that counts.
The first game that got me sold on adventures was Deponia and generally all of the Daedalic games.