I voted Lemmings, purely because it is a game that I enjoyed, one I was desperate to complete, and one that spawned so many sequels & rip-offs which I also enjoyed playing. I'm not sure if it is my personal favouirte on the list, but I think it is more deserving of winning than anything else here.
On a technical level it was an Amiga first, it was more original than most on this list and it gave the Amiga crowd an enormous sense of satisfaction knowing that it was eventually ported to basically every gaming system in the universe.
Out of all the games on this list this game is possibly the only one my mother has heard of.
And it also was the game that made some serious bucks for DMA Design, which in turn led to them founding Rockstar Games, which in turn led to GTA San Andreas
Jim (Resident GTA San Andreas Fanboy)