I know some of you have backlogs going back to the 80s. Let's just focus on this generation--I'll count PS2 since it is still very active--and on games you actually want to play to satisfaction not to completion to make it simple or whatever criteria you choose. Most of the games I play until I complete them, whether that's beating the final level, race, track, or boss. I gave up on 100 percent completion a long time ago.
I love fighters but I play them with friends constantly and there is nothing to complete obviously, unless you prefer playing single player modes. My backlog has just been growing and growing. I'll probably never finish it. Maybe during the summer months when game releases tend to slow down.
360:
Shivering Isles - Complete
Portal - Complete
CO4- Complele on the default difficulty
Halo 3 Complete on Legendary
Rockband - Complete World Tour and individual instruments
Lost Odyssey - Completion
Burnout Paradise - Elite license
N+ - Complete al 50 single player levels
P33
Hot Shots Golf 5 - Unlock everything. Long term project for those familiar with the series
Resistance -Complete once
Ratchet - Complete once
Wii
No More Heroes - Complete
Zack and Wiki - Complete
PS2
FF12 - Complete
Valkyrie Profile: Silmeria - Complete
For my portables I just play the games to completion. I will play the additional difficulties for Ninja Gaiden DS, though.
PSP
Valkyrie Profile: Lenneth
Ultimate Ghouls and Ghosts
FF: CC
God of War: COO
Wild Arms: XF
DS
Phantom Hourglass
Ace Attorney 5
Ninja Gaiden DS
Bangai-O
Space Invaders Extreme