NES - Kirby. - Colourful, rotation and scaling of sprites.
SNES - Starfox. - Polygonal 3D.
N64 - Perfect Dark. - Lense flares, shadows, reflections and more.
OG Xbox - Morrowind. - Open world, Bethesda actually "rebooted" the console during load screens in order to save on memory.
Xbox 360 - Halo 4. - Impressive texture work and subsurface scattering (Ray Tracing) to give characters some incredible detail.
Gameboy - Links Awakening DX. - Really large and impressive world for the old 1980's hardware, definitely doing more than the NES Zelda game ever did.
Nintendo 3DS - Monster Hunter Stories. - This game was larger and more detailed than it had any right to be.
Playstation 1 - Final Fantasy 8. - Large and detailed maps/screens/2D art work combined with FMV to seamlessly transition between both resulted in some visually impressive moments for the platform.
Playstation 3 - Uncharted 3. - Impressive visuals for the hardware, using Screen-space effects to the max.

That's my pick.

Here's another I just thought of. Half-Life 2 on the original Xbox. A game that we're celebrating how perfectly it holds up 20 years later was somehow able to run on a home console of that era.

Solaris on Atari 2600. Had more going on than some NES games did.

This.

They aged fantastically well, also.

Kinda cliche but the first time I played Donkey Kong Country on the SNES I was blown away.

"Get ready to take flight with the hottest Super NES cart yet! Starfox uses the all-new Super FX chip to create smooth polygon graphics so real, you can feel the banks, turns and explosions!"

$59.99 (before March 23rd)

I really appreciated those old consoles for what they offered - I find NES (Kirby also had additional hardware in its cartridge) and SNES to be, well, "cost effective" hardware wise, but that philosophy of allowing cartridges to have more hardware and thus making its "host" more powerful (in the case of Super FX, WAY more powerful) is something that was missing from later consoles.

Yeah Starfox (Starwing here in PAL) was the first game I ever played so I didn't realize at the time what a breakthrough it was, but seeing polygonal 3D on the 16-bit SNES must have felt mind-blowing at the time.

On Wii, the enormous fantastical landscapes of Xenoblade were like nothing else on the system, I couldn't believe all that was running on just 88MB of RAM.

Zangeki no Reginleiv, a Japan-only Wii game that was never officially localized, also seemed beyond the capabilities of the hardware, pulling off vast battlefields with countless enemies including kaiju-size ones that you could chop to pieces with motion plus. Such a shame it never came westward.

Donkey Kong Country on SNES
Donkey Kong Land on Gameboy
Street Fighter Alpha 3 on GBA
Resident Evil Revalations on 3DS

Based on the frame rate that certainly was beyond the capabilities of the Wii lol.

The bigger battles like this stage do chug a fair bit, but given the stuff it's pushing it's a miracle it doesn't burst in flames lol