Depends on what criteria you want to base the 'best game' argument on.
From my point of view, remember that's all it is.....
Longevity, now if a best game were based on longevity, then I might have to say Lords of Midnight and it's sequel Doomdarks Revenge, what are they you all cry? a couple of turn based stratergy/war games from around 1984, I played them to death on my old 8bit home comp, I then played them on the amiga and stuff when people started writing their own versions of them, then on the pc and now some guy has written a great conversion of both of them for the GBA, so I can carry them in my pocket and start up the war of the solstice whenever I like, so 20+ years of gameplay is not bad...
Now if you wanted playability, a game that you can pick up anytime of day and get straight into it , then I'd say Doom, everyone knows how to play it, it's on just about every format out there, it's easy to play , great stuff.
If you were talking about out and out solid gameplay that keeps you hooked, then I'd go with GTA Vice City, I don't think I've ever played a game as much so often, kept me occupied for months, and during that time not a single other game made it to my console, just the sheer open ended nature of it made it a joy to play, some days I'd knock out a few missons, others I'd just drive around doing mad stunts, others I'd spend looking for packages etc etc etc. Solid..
For Happy Wow Great Amazing memories, I'd say FFVII, a revalation in gameplaying at the time, stunning visuals combined with gripping plot, a game where I just wanted to see, do, collect, meet everything and everyone , I was quite sad when it ended.
So much to choose from it's hard to pick an all time fave.