The Wii is like a band that has a couple handfuls of really good songs, but most of the songs put out are filler made to capitalize on the overall success of the band rather than deliver a quality experience. And then there are songs that should have been great, but came out bizarrely bad.
In this case, the handfuls of good songs would be Super Mario Galaxy, Donkey Kong Country Returns, Super Smash Bros Brawl, Metriod Prime 3, etc. You know, the good games that are usually first-party Nintendo.
The filler would be the mountains of low-quality shovelware that the system is steeped in.
The bizarrely bad songs would be stuff like Metroid: Other M. Seriously, what happened there?
Don't get me wrong, I love my Wii. It does have some really good games and I love that it is a backwards-compatibility powerhouse. It can play Gamecube games and it can download the best games from systems of Nintendo's past. In that regard, the Wii is great.
But as a machine that consistently provides high-quality current gen experiences? The Wii is an utter failure compared to the PS3 and 360. Because it's underpowered compared to those two, it's missed out the big third-party games, and the few-and-far-between great first-party offerings from Nintendo aren't quite enough to keep it highly relevant from a current-generation gaming perspective.