The Wii is a gaming machine, and most of these games aren't story-heavy and intriguing which fuels traditional gamers to play more and more. What's so great about the wii is that it doesn't use a traditional controller, making less complicated and therefore more enjoyable for people don't play video games.
If I received a dollar for everytime I heard my mom say "where's the A button." before the Wii, I'd... probably wouldn't be a very rich person because she didn't want to play again because of the controller. At least with the wii, the controls are simple because they require actions that are done in real life, therefore simple to most.
Whether or not the Wii can be called "fun" for people can't be truly be determined but for the most part, normal people seem to enjoy it.
Not everyone wants an extensive story with realistic graphics, it's more about being able to PLAY foremost.
Pixel Art can be fun.