I was just recently able to get my hands on a Wii and have not been able to exhaust the extent of Nintendo's "core" franchise games by the slightest. In fact, I'm only half way through my second Wii game, Twilight Princess. I wouldn't be interested in these games if they took 18 months to develop, and I am completely open to new franchises that appeal to my demographic, should Nintendo go that route. Let's face it... how much Mario, Zelda, Donkey Kong and Starfox can you stand playing over a span of  20 years?

I don't think the "core" gamers need to worry due to the fact that there are plenty of high profile 360/PS3 and PC games (c'mon, you've got to own at least one other gaming capable system than the Wii if you're reading this) coming out soon. That is unless they're one of those platform fanboys of course .

Also, I think I'll be keeping my Wii forever, like all my consoles back to the NES.

EDIT: It also seems fit (pun not intended) to mention the Wii Motion Plus controller accessory. We could see some new franchises from Nintendo that require the precision of this peripheral. I think I'm excited about it because I don't know its limits yet.