You started gaming on the 360? 

Actually, I meant finished to "full gamerscore" or "platinum trophy" and/or whatever Steam counts.
I'm not always fond of Trophies and Achievements, but they have changed my perspective on gaming; I think I'm trying to look at my own compulsive, collector tendencies and applying them to this model of "completion."
If it's what game did I first completely finish, it's probably
Zork I. If we're limiting this to games with graphics, it was
Karateka.