Nintendo's best games have been pretty much on par with Sony's this gen which wasn't the case last gen when they were releasing games that didn't really improve over the games on the N64 in any significant ways other than Metroid Prime and in the previous gen when Nintendo had a handful of amazing games but was blown away by both the PS1 and even the Dreamcast in its short time on the market as far as the sheer amount of outstanding games on the market.
The Wii has two problems. It isn't powerful enough to make games that look as good as the best games on the 360 / PS3, so the games on the Wii to look as good as those on the other systems must have a high degree of art direction in them see Muramasa, Fracture, Kizuna, No More Heroes, and Madworld which all studios probably aren't qualified to deliver. And, it is stigmatized in fan circles because the best games on the system like Mario Galaxy, Metroid Prime 3, No More Heroes, Zelda: Twilight Princess, Okami, and Zack and Wiki haven't been the system's biggest selling titles while cheap simulators that appeal to the mass of people (just as fluff music appeals to the mass of people while more meaningful alternative or punk music doesn't) like Wii Sports, Play, and Fit have been the highest sellers on the Wii.
Super Smash Brothers Brawl is an exception to the best games on the Wii haven't been the system's best sellers thanks to the popularity of all of Nintendo's colorful characters while Mario Kart Wii has walked the line as being the best selling core game on the Wii yet carrying many of the same qualities as the simulators and not having really seen much improvement over past games in the series, thus creating a more average appearing critical appreciation of itself.
Heavens to Murgatoids.
