The game that came with the NES!
Mainly because it was for a long time the only game I had on my NES, and because it's endless replayability!
How many times haven't I tried shooting the dog, reaching level 100 in the clay pigeon mode of duck hunt, effortless tried to conquer that last castle of mario bros.
I never finished Mario Bros, to my shame.
I always died at Browsers final showdown.
I cried a lot in that final stage, get angrier by the time I died.
Damn you Browser! Damn you to hell!
Too bad I lost my NES, and lend out it's cartridges never to be returned to me.
I definately am going to by this game again, for nostalgia, and the replayability.
And so that I finally can beat bowser, on his home turf, the NES (did it emulated, but that doesn't count with the instant saves one can make)