I’d echo what others have said. The Wii is a great party console, great to drag out with a few mates round, beer and pizza and an evening of bowling or some such. Where it wins is easy to play, quick round gaming like bowling and such. By the time you’ve ponied up for the thirtyseven controller components you’ll need ideally for four-player grooviness though, it’s not as cheap as it first looks.
If OTOH you want a console with meatier games you can get your teeth into and sink hours playing, you really need to be looking at the 360 / PS3 instead. I’ve just completed the main storyline on Final Fanstasy 13 and it’s showing something like 70 hours’ total gameplay, with a large chunk of game still left to play. By comparison, I can’t see myself putting seventy hours into Nintendogs. But then of course, I’m equally unlikely to get a couple of mates around and sit playing Fable III on the Xbox all night.
So yeah. The Wii is a groovy thing, but it may or may not be a good purchase for you depending on what you expect out of it. My OH has been after one on and off for a while now, largely for the Wii Fit, but I’ve not bought one purely because I’m fairly certain that the novelty will wear off inside of a week and it’ll be a white elephant.