So I had a go on Steve's Wii this afternoon at Dan's sumptuous paella-fest. I am by no means a console player -- I've never owned one, or played any game on one for more than about 10 minutes without getting bored -- but that thing is a whole new ball game. Playing tennis that feels like playing tennis, from the motions you make to the sounds on the court, is so totally different from the usual button-A-means-you-jump dynamic that it needs a different name: low-fi virtual reality, or something.
So in summary: they're amazing, and even non-gamers will want one. Well done, Nintendo, for making a console game seem interesting to me for the first time since, well, the original Nintendo system.