1st - Projekt: Passion, SAndrA is
Then Being a DIK - the best virtual "college experience", at a time when the real one has noticeably sagged in recent years
First game, that was not some animation with "Faster", "Slower, "Cum" buttons: Fatal Relations (JAVN), which was already very old and could barely install it on Windows Vista
First game that really clicked for me: Witch Trainer
If I remember correctly it was Dating my Daughter by mrDots but I played soo many games the first year I found adult game forums that it might have been another game I played before DMD. I am happy my first game wasn't Being a Dik though because I'd probably be pretty dissapointed in other games if that was my first with how good it is.