I totally love the Kinect for losing weight (and I'm excited to see what they put out for regular video games.)
I have Your Shape:Fitness Evolved and I love it! It's already helped me lose 6 pounds and it really gets me sweating. I also have Kinect Adventures that came with the Kinect. If I play that one long enough it'll get me warn out.
I tried Dance Central, but I couldn't really get into. But, I suppose I've never really been into "hip-hop" dancing. I also tried The Biggest Loser game demo, and it totally kicked my butt! I couldn't even finish the demo because of how hard it was for me. ... Needless to say, I'll probably be getting it at some point, haha.