PS1 = Oddworld: Abes Oddysee (& Exoddus). I find these to be the most beautiful games on the PS1, the best looking side scroller of its era.

PS2 = God of War II. Came out after all the next gen systems had already released and it still held its own visually.

PSP = God of War: Ghost of Sparta. Can compete with even the best looking PS2 games.

PS3 = God of War III. Yeah,  God of War: Ascension looks slightly better but GoWIII was the first PS3 game to blow me away and only GoW:A looks better, nothing else has topped it, not even UC3, KZ3 or TLoU.

Xbox = Splinter Cell: Chaos Theory. Always thought this looked stunning, the only game I played on the Xbox that wowed me.

Xbox 360 = Gears of War (series). The 1st introduced me to next gen visuals, its successors got increasingly better looking and GeoW:J is very good looking.

Gamecube = Luigis Mansion. Always loved the look of this game.

Wii = Super Mario Galaxy 1 & 2. These are very good looking games, it's a shame hardly any developers tried to use the Wii's full potential.

At the time, I felt like Shadow of the Colossus and Spider-Man 2 had realistic graphics.

I take it as what games were the most demanding for the system they were on?

In any case, the titles bolded in italic are the ones I think look best. The others are contenders.

NES:

- Kirbi's Adventure (That game looked like a SNES game FFS!)

- Dragon Quest IV

SNES:

- Street Fighter Alpha 2

- Star Ocean

- Seiken Densetsu 3

- Donkey Kong Country series

- Super Mario World 2: Yoshi's Island

- Tales of Phantasia

- StarFox

Sega Genesis:

- Vectorman

- Virtua Racing

- Comix Zone

- Gunstar Heroes

- Sonic 3 and Knuckles

Nintendo 64:

- The Legend of Zelda: Majora's Mask (no contest there)

Playstation:

- Tobal 2

- Final Fantasy IX

- Metal Gear Solid

- Einhander

- Gran Turismo 2

- Chrono Cross

- Tekken 3

Saturn:

- Guardian Heroes

- Panzer Dragoon Saga

- Knights Into Dreams

Playstation 2:

- God of War 2

- Gran Turismo 4

- Final Fantasy XII

- Dragon Quest VIII

- Metal Gear Solid 3

- Grand Theft Auto: San Andreas

- Shadow of the Colossus

Sega Dreamcast:

- Shenmue series

- Metropolis Street Racer

- Jet Set Radio

- Phantasia Star Online

- Skies of Arcadia

- Sonic Adventure 2

Gamecube:

- Star Wars Rogue Leader: Rogue Squadron 2

- The Legend of Zelda: Twilight Princess

- F-Zero GX

- Metroid Prime 2: Echoes

- Resident Evil 4

XBox:

- Ninja Gaiden Black

- Doom 3

- Fable

- Project Gotham Racing 2

- Halo 2

Wii:

- Muramasa

- Super Mario Galaxy 2

-Donkey Kong Country Returns

- The Last Story

- Xenoblade

- Metroid Other M

- The Legend of Zelda: Skyward Sword

XBox 360:

- Halo 4

- Forza 4

- Crysis 3

- Metro: Last Light

- Bioshock Infinite

PS3:

- Gran Turismo 5

- God of War 3

- Uncharted 3: Drake's Deception

- The Last of Us

- God of War Ascension

- Crysis 3

I deny it that. I think Ocarina of Time and Majora's Mask looked better graphically, and they didn't differ from any draw distance issues. Conker's Bad Fur Day was also AAA.

Turok IMO wasn't special. Short draw distances really takes away from the experience. Even up close things don't look that amazing.

Doom (SNES)

DKC, Xenoblade and Final Fantasy III (NES).

I have to change the choice, Star Wars Rogue Squadron II is the best graphic showcase any system could wish for. Considering it was a launch title makes it even more of an amazing feat.

Yeah, RS2 was absolutely jaw-dropping back in 2001, there wasn't a better looking game on the planet.

I remember seeing it on a TV in a game shop and thinking, "that has to be pre-rendered, there's no way that little box is generating that!"

The sequel, however, pushed the system even further.

Battlezone on the Atari 2600.

Donkey Kong Country
Metroid Prime
Super Mario Galaxy 1 and 2
Gran Turismo 4
Resident Evil 4 Gamecube
Metal Gear Solid 3
The Legend of Zelda: Majora's Mask

Edit: Super Mario RPG: Legend of the Seven Stars