Now I've defended the Wii on these forums before and being the ultra Wii fanboy snerd I am, I'll defend it again as I feel the Wii is definitely a step in the right direction for modern gaming.
The latest criticism that's been used against the Wii recently is "waggle". First it was two Gamecubes taped together, then it was the mini-games, and now the hip thing to say against it is how you play games by waggling controller. If you actually think about the games, there really isn't that much waggle motion that's being used. Do you simply just waggle to play Wii Sport's Bowling? Marble Mania? Metroid Prime 3? Good luck trying to beat those games just by waggling the controller. Granted there are some gimmicky games that just waggle the controller, like Twilight Princess (a game not exclusively designed for Wii), but sometimes waggling isn't even a bad thing. For instance to do the spin attack in Super Mario Galaxy you can just shack the controller in any fashion and it will execute and unlike Zelda, it actually feels really nice and appropriate and is very simple to do.
Just as I predicted last year, I said by the end of 2007, the Wii would have a pretty nice line up of games and online play would improve and I think both points are right. Most people don't realize it, but the Wii actually has a decent amount of good games right now and since all the attention is focused on Metroid, Mario, and Smash Bros., these games get ignored. Aside from the big exclusive Metroid Prime 3 and Super Mario Galaxy, other games worth playing would be (and not limited to):
Link's Crossbow Training (surprisingly a really good game)
Zack & Wiki (a revival of classic PC adventure style games)
NiGHTS Journey of Dreams (faithful to the original)
Guitar Hero III
Ghost Squad
Resident Evil Umbrella Chronicles
Geometry Wars: Galaxies
Fire Emblem: Radiant Dawn
Trauma Center: New Blood
Batallion Wars II
Super Paper Mario
With at least three of those games offering true online play. While online play for Wii still isn't great, I think it has definitely improved since the beginning of the year and more and more games, both first and third party, are jumping on the online bandwagon. But personally, I think real life multiplayer is way more fun than online anyways.
There is one main (and obvious) advantage Wii has over the other systems and that's it's ability to attract everyone to play it. My parents love the damn thing so it's great to play games with people that I haven't really played with before. Oh and another advantage is that Wii will get you chicks while 360 and PS3 gives you zits.