Adults? women? kids? teens?
Gamers.
The Wii right now is an exceptional propostion for people who are and have been gamers for a long time, because of the excellent all-encompassing back-catalog that is the Virtual Console, and because of the new set of mechanics to explore in native Wii games. That's what gamers like to do: adapt to and master new mechanics. It's actually my favourite definition of gaming.
Casuals who walk by and give Wii Sports a shot will most likely enjoy it to some extent. It begs the question if Wii Sports is worth the price of admission, or, even if you're sure you want to game, if another console would represent a saner investment. But it is attractive to that broader audience, and there are many in-store demos going on right now that feature Wii Sports, and it really is the strongest pull to current non-gamers.
OTOH it's also something that most "real" gamers enjoy after they get over the facts of weak presentation and non-existant plot. Wii Sports might make a non-gamer "get it", see that there's satisfaction in doing well
according to a computer program's rules, which would bring them closer to being gamers. That's Satoru Iwata's market expansion right there.
Predetermined gamers already know how the stuff works, and for them Wii Sports is a challenge in different mechanics at first, but the appeal quickly shifts to the physical excercise. It's a brilliant excuse to play another round of tennis or boxing.
So the two groups come to the machine for different reasons but they'll both end up playing Wii Sports on a level field. And then they can turn to the more complex "fun" games such as Super Smash Bros or to the more complex "serious" games such as Mario 64 on the Virtual Console, or to the fuller experiences such as Zelda and Metroid. Nintendo will soon have most bases covered, with the obvious exception of graphics.
So it's really not hard to find people who'd enjoy the Wii. The much harder question is: was it necessary to make the Wii such a low-cost machine? IMO no.
Nintendo has a way with mechanics-driven gaming and Wii Sports drives this point home just as well as Zelda, New Super Mario Bros, whatever. They do it again and again. It's their area of expertise, Nintendo pretty much runs rings around everyone else and it's only proper that they focus on it. However, I believe that certainly you
can make a brilliant mechanic-driven game
with excellent graphics. Good graphics cost money, yes, but graphics are not some malady that could pull the other aspects of a game down, if you leave the other budgets intact.
I would have been willing to pay the 30€ extra it would have taken to double Wii's hardware specs all-around (CPU, graphics, memory, bandwidth). But it's still, as it is, a platform that is fun to play.
And I think it's going to be significantly more successful than the Gamecube, both in terms of absolute metrics and in terms of market share. It's just so appealing.