For me personally:

2009

Killzone 2
Batman Arkham Asylum
Uncharted 2
Infamous

Objectively (I didn't have a console yet in 2007 so I played a couple of these in later years):

2007

Mass Effect
Bioshock
Orange Box (incl. Portal)
Uncharted
Overlord (personal favorite)
Peggle
FIFA 08 (first in a series of great FIFA's)
R&C Tools of Destruction
Crysis
COD4
wii games such as Super Mario Galaxy?

2009 so far:
- Demon's Souls
- Left 4 Dead 2
- Uncharted 2
- Ratchet & Clank: A crack in time
- Killzone 2
- Batman Arkham City
- Assassin's Creed 2
- Resident Evil 5
- Borderlands

But 2011 will be better
- Dark Souls
- Gears of War 3
- Uncharted 3
- Deus Ex: Human Revolution
- Assassin's Creed: Revelations
- Batman Arkham City
- The Elder Scrolls: Skyrim
- Portal 2
- Dead Space 2
- LittleBigPlanet 2
- LA Noire
- ICO & SoTC: Collection

I <3'ed 2010. Great year...

Super Mario Galaxy 2: Favorite game of the generation, 2nd favorite game of all time. Boom!
Donkey Kong Country Returns: One of the best 2D Platformers I've played... and that's saying something.
Epic Mickey: It was like playing through my childhood... so many great moments in this game for me.
Kirby's Epic Yarn: So. Freaking. Adorable. And the gameplay was super solid too. Fantastic game.
Pokemon HeartGold/SoulSilver: Remakes of one of my favorite games ever.
Castlevania: Lords of Shadow: Fun action game with an incredible atmosphere.
Super Scribblenauts: Improves on its predecessor in every way imaginable and adds adjectives. Giant zombie pandas!
Cave Story: Awesome 2D Action Platformer with gorgeous sprite graphics and a fantastic soundtrack.
Sonic Colors: Not just the best 3D Sonic ever, but a great game overall. Sonic's back!
No More Heroes: Desperate Struggle: Sequel with more insane bosses and great humor.
Endless Ocean: Blue World: Nothing else like it. So serene and beautiful.

Yeah... amazing year. 2007 comes close though!

Nobody is mentioning 2009:
Batman:Arkham Asylum,Modern Warfare 2,Assassins Creed II,Uncharted 2,Killzone 2,Infamous,FIFA 10,Forza Motosport 3,Left 4 Dead 2,DiRT 2,Street Fighter IV

2010 is second for me with:
Mass Effect 2,Red Dead Redemption,Halo Reach,God of War III,Assassins Creed Brotherhood,Need for Speed:Hot Pursuit,Call of Duty:Black Ops,Battlefield:Bad Company 2,FIFA 11,NBA 2K11,Heavy Rain,Gran Tursimo 5,Super Street Figher IV


2011 is gonna be best with:
Battlefield 3,Killzone 3,Gears of War 3,Uncharted 3,Modern Warfare 3,Resistance 3,Crysis 2,Portal 2,Dead Space 2,Infamous 2,Elder Scrolls V:Skyrim,Assassins Creed:Revelations,Batman:Arkham City,LA NOIRE,Need for Speed:The Run,FIFA 12,NBA 2K12,Saints Row 3,Motorstorm:Apocalypse

The longer this gen on the better it gets ;)

2005,2006,2007 and 2008 pretty much except 2007 and 2008 had previous iterations of some of the current games but worse like:

2007:Mass Effect,Uncharted,Modern Warfare,Assassins Creed,Halo 3 and Elder Scrolls IV

2008 was pretty much dull but with one exceptional game:

GTA IV 

I really wasn't a fan of 2004-6. And I'd rather not vote for future years, because we don't know what will finally end up being released, or even how good the games will be.

2007:
BioShock
Mass Effect
Ratchet: ToD
Uncharted: Drake's Fortune
Portal
Call of Duty 4

2008:
MGS4
LittleBigPlanet
Left 4 Dead

2009:
inFamous
Uncharted 2
Dragon Age Origins
GoW Collection
Killzone 2

2010:
Mass Effect 2
Red Dead Redemption
Black Ops
God of War III
Heavy Rain
Civilization V
AC: Brotherhood

I think 2010 just about edges out 2007.

2012 for me. With SSX, Soulcalibur 5, Transformers War for Cybertron 2, The Lord of the Rings: War in the North, Star Wars: The Old Republic and many other games. I'm really excited.