I have to go with 2001.
I really believe that Grand Theft Auto 3 and Halo brought gaming to the masses moreso than anything previously and anything since.
I also dont know for certain but I believe Gran Turismo 3 was one of the highest selling games of all time. It was one of the first console games I am aware of that looked photo-realistic.
It was a good year in general obviously for gamers what with the releases of the Game Boy Advance, GameCube, and Xbox but the games is what people talk about more than anything.
This was also the first year where the current 3 relevant console makers first started competing against one another. The landscape hasnt really changed much since Sega started going third-party. I guess other than Sony introducing a competitor to Nintendo's portable.
The only other year I can think of is 1995 just because of the release of the PS1, a console that did everything right at the time and completely dominated the market henceforth thereafter.