My grandparents own a Wii. Apart from serving as grandchild entertainment, they use it to play golf-games.
There are golf-games for the Xbox 360 and the PS3 too, but I really don’t see my grandparents playing those, very simply because of how differently golf games would be interacted with on those platforms. On the 360 and the PS3 you play golf with your controller, mashing buttons like you would control any other game. On the Wii, you swing the remote like a golf club. Granted, it doesn’t always work or respond the way it was supposed to, but it works.
For my grandparents, swinging a Wii Remote is a much more intuitive way to play the game than using buttons and thumbsticks. How to interact with a computer is not something we instinctively know, but something we learn as we use it. The aim of interaction design is to make human-computer interaction as intuitive as possible; it should aim to minimize the learning curve before the software is mastered.
I think the very different and more intuitive way of controlling the Wii is the reason it is so popular with people who otherwise would not play much games. The more intuitive something is, the more accessible it is. For example, an iPad is so intuitive in its usage it is perfectly accesible for my toddler siblings and cousins to learn to use and navigate on their own.
I definitely see the value of developing interaction design. Right now, most game accessoires just seem superflous, clumsy and broken to me, but I think the Wii demonstrates that intuitive interaction design is definitely a key into a market outside the usual "hardcore gamer" audience.
I play a fair amount of games and know approximately how to interact with a game when I start it. All console games tend to have the same sort of control scheme. Move character with the thumbstick, move camera with other thumbstick, A to jump, etcetra.
Portal 2 elegantly introduces how to jump. To experienced players it is not a tiresome way to be told again, and for new players it does the trick.
Games today are a lot more complex than the games I grew up playing, for better and worse. They let players move in three dimensions intead of two and the game play options can be very complex and diverse. Naturally, interaction design has evolved with them and it's really easy to see when you look at old consoles and controllers and compare them to what we've currently got.
The 1988 Megadrive's controller and the 2005 Xbox 360's controller.
I really like the game Skyrim, but I think the overly complex gear system is frustratingly disruptive. I often find myself forced to have to go into the interface in the middle of a battle and navigate trough menus to select the item I need. I don’t remember this being as frustrating issue in its predecessor, Oblivion, so clearly something went a bit wrong there.
Seriously even using the zipline is like brain surgery in this game.