SNES - Yoshi's Island and Super Starwars (tie), Yoshi's Island because its my favorite game of all time, its fking awsome and Super Star Wars because i beat it quicker than my friend who allways kicked my ass at games
n64 - Ocarina of Time, nothing else even comes close, the subsiquent 10-20 odd times i finnished it after that were all just as good
GCN - Skies of Arcadia (so far) my first real RPG that ive owned (not i finnished the Chrono Trigger ROM before i finnished this, but it doesn't count because roms are bad) this had an awsome story, with characters i enjoyed playing along with (figurativly speaking) im definatly looking forward to playing this through again in a year or two.
GBA - Pokemon Ruby, only cause Mario (the forum user) egged me on constantly to finnish it, and when i did it was well worth it, the end music is awsome
Amiga 500 - Secret of Monkey Island, my first game finnished ever, done all by my self, and its one of the best games around (i cant believe your felicity)
486 - X-Wing, never fully finnished it, but i was pretty damn good at it untill i lost the list of codes needed to get past the copy protection, and then the discs, and then the computer later on

p1 233 - Monkey Island 2 LeChuck's Revenge, awsome sequel to an awsome game, this game really made me fall in love with Monkey Island, AND i finnished it before dad, i had some serious gloating todo

out of all of those though i think Yoshi's Island takes the cake, its my favorite game of all time