Here are the ones I can remember, on top of the ones many others mentioned:
StarFox - made me want a SNES over Genesis
Night Trap - yea, kind of embarrassing, I guess, but FMV really was super impressive back then
Virtua Fighter 3 - my local arcade had this game, and it was the best looking game ever to that point.
Starsiege Tribes - When I got this running on my Voodoo2, it was so sharp, with the far horizon and rolling hills, really amazing looking game at the time.
Age of Empires 3 - weird pick, I know, but I was blown away at how much better it looked at the time compared to every other 3D strategy game, in terms of shadows, character details, animations, etc.
Crysis - came out 12 years ago and it's still one of the best looking games, makes no sense.
RDR2 - I was really stunned at how amazing this game looked on Xbox One X, it's really incredible.