A bunch.
1. I quit Majora's Mask very early because I couldn't do some stupid mini-game that wasn't required. Had flashbacks while playing Arkham City's AR missions early in the game, though fortunately I finished those.
2. I never really got into Call of Duty until Black Ops, and even that wasn't until several months after it was released.
3. I've never played beyond the first Coloussus in Shadow of the Colossus. Three or four times I've started it, killed the first one, stopped, and then never gone back. This is one I plan to fix, as I've got the HD collection.
4. Started, but haven't played much of, the following (note that if the game is the first of a series, you can bet I haven't played any of the sequels either.):
Bayonetta
Dead Rising
Heavy Rain
God of War 3
Demon's Souls
Gears of War
Metal Gear Solid 2
GTAIV (though this one I tried...I just hate it)
Halo 3