I like achievements. It gives a kind of purpose to obsessive completion of games. I know gamerscore is worthless, but at least now you have something to show for all those hours
wasted. Only I know that I 100%'ed all those old Final Fantasy games, just as an example. :/
Anyway, Retail 100%:
Oblivion, Fallout 3, Assassin's Creed, Spider-man Web Of Shadows (just NOT a good game, at all),
Resident Evil 5 - minus the DLC.
Arcade:
Portal: Still Alive, Monkey Island SE
I'm SO close to 100% on too many games, highlights being, Bioshock, Bioshock 2, Borderlands (need the DLC first...), the Orange Box, Left 4 Dead, Left 4 Dead 2, Lost Odyssey, Prince of Persia, and Soulcalibur.
I'm getting there, anyway..