Zelda
Zelda Link to the Past
Zelda Ocarina of Time
Zelda Majora's Mask
Zelda Wind Waker
Zelda Twilight Princess
Morrowind
Oblivion
Call of Dtuy (the first one)
Call of Duty 4
Baldur's Gate
Baldur's Gate 2
Diablo 2
Halo (the first one)
Half-Life
Half-Life 2 (plus the episodes)
Dragon Age: Origins
Mass Effect
Mass Effect 2
Heavy Rain
God of War
God of War II
Fallout
Fallout 2
Fallout 3
Metal Gear Solid (the first one)
Jak and Daxter
Jak 2
Age of Empires II: The Age of Kings
Company of Heroes (plus expansions)
Fable
Fable II
Fire Emblem
Fire Emblem: Shadow Dragon
Resident Evil 4
Sonic Adventure
Sonic Adverture 2
Super Mario Bros.
Super Mario World
Super Mario 64
Super Mario Sunshine
Super Mario Galaxy
Donkey Kong Country
Donkey Kong 64
Runescape
Runescape 2
If you couldn't tell, I went by series.
All of these games left a HUGE impact on my mind, one that I will carry for the rest of my life.