Some friends of mine at work have them and say it's the most fun they've had with a gaming system in a long time. I'm intrigued by it, here are some highlights:
*Motion capture controller. When playing a tennis game, you swing it like a tennis racket. When bowling, you act like you're bowling. It's a high resolution motion capture device, so the way you physically do stuff actually controls what the character does.
*Virtual console. It has a built in emulator that can play games made for other Nintendo systems + NeoGeo. They're releasing 4 games a week, from Super Mario Brothers to GameCube and Nintento 64 games, etc. They sell them for a few bucks each.
The system looks like it's more social, ie, everyone is involved. Sounds like a good match for a family.
Oh, it also has built in 802.11 and bluetooth, so it can use your wireless internet connection without running new wires.