NES: Kirby's Adventure. Could have passed for a SNES game without weird screen-edge tearing of SMB3.
SNES: Probably Yoshi's Island. It needed the Super FX 2 for the effects it was pulling off.
N64: Tough call between Perfect Dark, Battle for Naboo, and Conker's Bad Fur Day. PD has extremely detailed environments, BFN has astounding draw distances and the most advanced particle effects on the system, and Conker has the best animation of any N64 game.
Gamecube: Again, tough call between Rogue Squadron 3, which was like Rogue Leader but with more ships, better lighting, and better explosions, Metroid Prime 2, which was like Prime 1 but with better textures, and Resident Evil 4.
Wii: On a technical level, I think it's between Other M and Conduit 2. Those are games that could legit pass for 360 games in places without relying on cell-shading or some other art change to make them less realistic.
Wii U: Breath of the Wild. It needed the system's full 2 gigs of RAM.
Switch: On a technical level I think Witcher 3.