I remember a few from various stages of my life (born 1984).
Seeing the demo footage of Sonic 2 in Woolworths and thinking the leaves falling down in Aquatic Ruin zone was so cool and advanced.
The original Sega arcade of Virtua Racing with the moving cars completely blew me away.
I remember my uncle loading up Cannon Fodder on his Amiga, and a REAL song with REAL music came out, along with REAL photos. I was amazed haha.
A few years on I remember a PlayStation demo disc having promo footage of the first Gran Turismo and it looked so real to me, I watched it over and over. The first Driver on PS1 looked absolutely amazing to me also.
I remember my brother telling me about Wolfenstein 3D. I insisted that something like that, that moved smoothly at your command in any direction instead of in clunky 90° turns and blockwise steps, was impossible with the current technology.
I was wrong.
you were right, the computers couldnt do the math in time. the trick was to precalculate the sin/cos tables for angle steps into tons of lookups instead.