I don't think I play enough new games to really make lists like this. Now that I have a GameFly account, maybe this will change.
Anyway, if you're talking about bets games of all time, the list starts with Tetris and includes either Dragon Warrior III or IV or both.
Best games of 2004 includes Katamari Damacy, Monster Rancher 4, and Paper Mario: The Thousand Year Door along with the usual suspects that everyone will name.
My best games of 2005 so far won't inlcude XBox, unless someone wants to be kind enough to donate one. As far as PC, PS2, and GC go:
PS2:
Mercenaries
Winning Eleven 8
Gran Turismo 4
Tekken 5
GC:
Nothing! Unless you want to consider Donkey Konga 1&2 as a single title, just because bongos are cool.
PC:
Sims 2: University
Darwinia
And that's really it so far. I haven't really played that much this year though, and it's still early, so ask me again in a few months.