It all depends on your style with games. When I look at a video game the types that pop in my mind are of course NiGHTS, Sonic, Mario, Zelda, Fantasy Zone etc.... I like games where people are really creative and come up with things that you would never see in real life. That's what a great game to me is something that takes you away from the real world for a while.
So a game that I would consider the greatest of all time is,
Toe Jam & Earl Panic on Funkotron! (Thought I would of said NiGHTS huh
)
But Toe Jam and Earl had beautiful level design, great game-play, one of the best soundtracks I ever heard, and a great story.