The best year in my opinion would have to be 2004. Almost EVERY game that was considered great before this year, had a sequel, and almost all of them turned out to be better this time around. Like this :
Before
Halo, Metal Gear Solid 2 ( And 1 ), Half-Life, GTA3 ( And Vice City ), Metroid Prime, Warcraft 3,
After
Halo 2, Metal Gear Solid 3, Half-Life 2, GTA: San Andreas, Metroid Prime 2, World of Warcraft, Burnout 3 ( C'mon! I know earlier editions might not have been 'great' (Even though I did enjoy Burnout 2) ( Too many inside curves lol), but I can't make a 2004 list without including Burnout 3 on it! Can't you go to jail for that? )
Oh, and these games aren't listed from 'most' favorite to 'least'. These are just the main ones that stuck out in my mind. ( So yeah, they're ALL favorites!
)
I can't remember another year that had sequel after sequel, each one being better than last time.