It was either Mortal Kombat or Asteroids, and I'm leaning toward the former. Don't remember if it clicked for me, but I was quite young at that time (7-8ish, I think), so probably didn't get excited. The first game with a plot I ever played (and remembered, at least) was Ocarina of Time, and I remember having my mind blown about how big the thing was. At first, I was expecting it to be over after the Great Deku Tree!