Nintendo 64

The best thing about Super Mario 64 is that it basically launched a game system by itself.  It was one of only 2 N64 games on launch day, but that was ok because SM64 is an endless display of level innovation and replayability.  I made it my mission to get every single of the 123 stars in the game, no matter how sadistic the endeavor became.  As for just playing and beating the game, my 3rd save file was deleted over 100 times to make room for another playthrough.  Every time, I didn't get all 123 stars, but Bowser was defeated 3 times and the Princess still was saved.  I was able to play the game on auto-pilot thanks an encyclopedic memory of each level and section.  The Original SMB may have created the modern games industry and Zelda: Ocarina of Time might be the best game ever made, but no game will ever come close to the hundreds of hours I put into Super Mario 64 and all the hours I still put in every year.  Now THAT is a great game.