Consoles - Star Fox - The Super FX chip thing they used to give 3d acceleration to the SNES was just nuts. I also competed in a local tournament right after it came out and won a shirt. To this day it is the only game I can play from start to finish on the hardest mode without breaking a sweat, usually.
PC - I played way too many games to remember which ones really wowed me. Freespace, Doom, Duke Nukem 3D, Indianapolis 500, European Air War and so on. It seems like every six months something would be released that surpassed everything before it and I suppose that isn't far from the truth.