Sounds fun. I'm a bit of an art style fan, but am not insane enough to pick a Nintendo game every year. I can't do this in a single sitting, so here is 2000 through 2005 first.
2000: Jet Set Radio
The cel-shading is pretty and stylish, and the game is fun to simply watch flow by. That's all. Honorable mention for Guilty Gear X
2001: Silent Hill 2
Despite what some may say, it is entirely possible for a horror game to have outstanding graphics that add to the horror rather than detracting from it. Silent Hill 2 is helped by its sticking to the style of the original, but also gets points for use of lighting, art direction for creatures and environments, and a solid job on the actual humans. Final Fantasy X also deserves mention, but loses points for feeling like less of a leap forward for the medium.
2002: The Legend of Zelda: The Wind Waker
I was tempted to place anything else here, but Wind Waker is too obvious. I do think Kingdom Hearts looked stunning though. Kingdom Heats deserves massive credit for both creating an art style that accomodates the wide range of franchises it tackles and making them all look good.
2003: F-Zero GX
So much speed and details and colors. Much zooming!
2004: Metal Gear Solid 3
Though it may not necessarily look THAT much better than MGS2, Snake Eater features more colorful and detailed locations than some dull oil rig could. Going into first person view at any given point gave visual treats. Honorable mentions for Halo 2 and Katamari Damacy.
2005: Resident Evil 4
2005 was a hard year, given how so many games took full advantage of their hardware. However, RE4 for the GameCube (not the somewhat uglier PS2 version) wins due to a combination of sheer detail of everything combined with some creative enemy designs and a style the melded the series horror tradition with action sensibilities. Honorable mentions go to God of War, Shadow of the Colossus, and Dead or Alive 4.
