Is that even a fair question? There's so many games that have made an impact or changed how gaming is done.

But if i stick with what the others are posting, my personal fav that I played through, LoZ Ocarina of Time. One of the first games I sat down and played through, and I just got sucked in. Fell in love with the whole of it. Not a thing bad about that game. FF7 was a really good one to. The story, and graphics at the time were fantastic.