I really like Kinect Sports seasons 1 and 2 with the random party play mode
Never know what you'll get!
Dance Central games are really good, but the Zumba one annoyed me a bit. I haven't picked up the Your Fitness game, but I did try the demo and it was pretty entertaining, but you could just spend $5 on a jumprope and not $60 on a game that makes you jumprope. Nike Trainer was a little intense for me, and I ended up panting like a dog in summer after a few seconds. So I skipped that one
Oh! And believe it or not, The Disneyworld game was pretty intense. It makes you flap your arms, jump up and down, move around in pretty insane ways. I was sweaty after that one!