My preorder doesn't come in until Tuesday buy my local best buy had a couple in today so I went ahead and bought it because the in-laws are in town.
I'm very happy with it so far... dance central is awesome... even got the mother-in-law up to dance to funky town... everyone had a great time with that. Kinect sports is okay... have only tried volleyball (fun), table tennis (boring) and track and field (fun and entertaining) so far. Also tried kinect adventures for ~30 minutes and had a blast doing the box breaking game (forget what it's called).
As a game system, I love it much much more than any of the wii games so far. The way you control it is absolutely amazing. It's damn near one to one... the show off and share stuff after a song/game is awesome when it puts your pictures on the screen doing whatever... the controls of the menu are cool. It'll be awesome down the line if/when it automatically signs into your profile when it recognizes you and if/when the voice control works (I haven't taken the time to set it up yet).
So essentially, 2.5 hours in, we've had a blast and it's better than I expected. I could see myself playing it by myself just to get better and practice dancing or something... otherwise it's a party game. I've had many a thoughts already of getting coworker X to play this game or friend Y to dance to this game... etc...