Dishonored (360) - popped the 10 pt. Achievement, Rogue, for assassinating 10 unsuspecting victims, which brought me to an even 100,000 Gamerscore at long last. I think my first cheevo was in the first Assassins Creed, so this seems appropriate.
n.b. Sceneman got to 100K a few years back, when we were gaming regularly. Demi probably has half a mil or whatever, but this was a long-standing goal for me. I can return to not caring about Achievements the same as PSN Trophies now.