Crap, I kinda want to get a Wii because I know my wife would like it a lot more than a 360 or a PS3... but the reason why I like systems is for the sports games. And GTA 4. I guess in the end I probably won't get anything and I'll be playing Goldeneye in 2012.
We have a Wii and a 360 at my house, and while the Wii got a lot of attention intially, now it basically collects dust. There's just not a ton of quality software out there for it. (outside of their first party titles) So many of the 3rd party games feel rushed and cheap. To me it appeals to an audience that is maybe a little more casual about gaming than I am.
I like twitch gameplay, realistic graphics, 1080p resolution, and online play. Those are things that Nintendo just isn't able to offer.
