gotta say

PC: starcraft, rise of nations, Halo: Combat Evolved, Pshychonauts

PS2: grandia 2, first 3 ratchets, Final Fantasy X

360: Halo 3, Far cry 2 (this game is badly under rated), left 4 dead (1st is better)

PS3: Little big planet, MGS 4

Xbox: Morrowind, Halo 2, Ninja Gaiden (ruined me for all other fighting/adventure games)

Dreamcast: Sonic Adventure, Power stone 1&2, skies of arcadia

Genisis: Shining force 1&2 (fire emblem, you don't come close)