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 was always more of a retro gamer even back in the day. 80s and 90s playing MUDs or Atari and getting an SNES late to the game. My computers were always hand me downs from my parents so i never really got into the best games when i was a kid.
But when i got that issue of PC Gamer with the demo of what Halo was going to be like, with the dinosaurs and cut scenes built into the engagement with your targets…wow i wanted to play that.