We bought one for our kids in early January and have loved every bit of it. Wii Sports is probably the coolest game ever included with a system. It is more cartoonish than real, but it is still tons of fun. Aside from Wii sports, we have Super Monkey Ball (which was great on the gamecube but turned out to be a dud on Wii. More because it was poorly designed than anything) Madden 07 which is a ton of fun to play, Tiger Woods 07 which is also a lot of fun and much closer to the real thing. And Wii Play which is basically an extension of Wii Sports with a bunch of mini games.
If you want a system that is a lot of fun to play and cheaper than the other options, go with the Wii. If you want a system that has killer graphics and online play, go with another console.