NES: Dragon Warrior
SNES: Chrono Trigger(best game of all time, up there with MGS and FF7)
PS1: Toss up.. Metal Gear Solid or Final Fantasy 7
PS2: .Hack
PS3: Doesn't matter if it's not out yet, it's definitely going to be Sons of the Patriots
PC: Diablo 1 and 2, Return to Zork, King's Quest
Xbox: sucks
360: see above