The Wii has higher potential for better graphics than the PS2 does, but the titles being produced for it tend not to make that much use of its potential. Probably the best examples of good-looking Wii games are Super Mario Galaxy and Smash Bros. Brawl, which are fairly significant steps up from their previous installments.
Here's close-up gameplay in Melee:
[img alt="Melee" src="http://o.aolcdn.com/gd-media/galleries/394/a_Super-Smash-Bros.-Melee.jpg" /]
And now Brawl:
[img alt="Brawl" src="http://cache.kotaku.com/assets/resources/2008/03/supersmashbrosbrawrev.jpg" /]
Here's Giga Bowser in Melee:
[img alt="Melee" src="http://farm4.static.flickr.com/3066/3061810319_0742d6cf0d.jpg?v=0" /]
And now Brawl:
[img alt="Brawl" src="http://i225.photobucket.com/albums/dd277/Kid_Dashm/Brawl/GigaBowser.jpg" /]
It's not as noticeable a difference between Gamecube graphics and Wii graphics as it is between PS2 and PS3, but it's definitely there. There's more polygons, the textures are a lot more detailed, and the lighting engine and shaders are a bit more sophisticated, even if they're not using normal/specular mapping. This is ESPECIALLY evident with Mario Galaxy.
Here's Mario in Mario Sunshine for the Gamecube...
[img alt="Sunshine" src="http://wiiconsumer.files.wordpress.com/2008/08/super-mario-sunshine.jpg" /]
... And now Mario Galaxy.
[img alt="Galaxy" src="http://www.gameplayer.it/novita/immagini/originali/super_mario_galaxy_arrivano_le_nuove_immagini_5.jpg" /]
Note that in Mario Galaxy he looks a liiitle bit less like he's made entirely out of plastic, mainly due to the lighting.
The Wii is actually a bit more potent than the original X-Box was, which still makes it a beefier piece of hardware all-around than the previous generation of consoles, even if it's not a huge leap ahead like the 360 and PS3. The trouble is that...
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[li]A lot of Wii games are just PS2 Ports or cross-platform games between PS2 and Wii, like Star Wars: The Force Unleashed, and therefore do not take advantage of the Wii's more powerful hardware as they are specced for the PS2[/li]
[li]A lot of Wii games are simple casual titles that don't involve much of a budget for bells and whistles like writing and artwork. There just isn't a lot to put together for something like Wii Bowling or Boom Blox.[/li]
[li]A couple of the Wii's best-looking games are BOTH ports from the Gamecube, those being Twilight Princess and Resident Evil 4, so there literally is no difference even with some of its quality titles.[/li]
[li]Nintendo themselves make hardly any effort to differentiate the new graphics from the old ones. You'll notice that while the shading on Mario in Galaxy is a lot better, they hardly made any changes to the overall design and details for Mario himself between Sunshine and Galaxy--and the same can be said for the environment art's construction, which tends to be very simple shapes. New Super Mario Bros. Wii, likewise, is BARELY an upgrade from its DS counterpart just because it's not necessary. The best Mario's ever looked is arguably in Brawl, where you can see the texture of every element of his costume.[/li]
[li]Because the Wii's best Wii-exclusives are still a really limited portfolio of titles (Nintendo's stuff), it's difficult to compare to something like the PS2, which represents a broad array of styles.[/li]
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Yeah, the Wii CAN do better... people just don't do it.
