Got a Kinect bundle for cheap during the holidays. I never felt incredibly compelled to play it, but I heard good things about Dance Central, and I loved DDR so I figured "Why not?".
I've played Fruit Ninja Kinect, which is a fun distraction to play with friends for about 15 minutes at a time. The Gunstringer has a lot of personality and charm, and the gameplay is decent, but it's largely forgettable. It's probably the best on-rails shooter I've played (besides Typing of the Dead).
But what has made Kinect more than worth the price of admission for me is Dance Central 2. I've already put in over 10 hours of dancing, and I'm surprised with my progress and lasting enjoyment of it. While it's probably not true to call it actual dancing, the routines are by far the closest video games have ever come to legit, full-body dance moves. The variety of moves fit the songs well, and I can consistently have a good time while achieving a rare (for me) full-body glistening sweat and cardio workout. I literally have to take a shower after hour-long marathon sessions because every part of me is moist and rather smelly. Feels good, man.
By the time I tire of this game, I'll have put dozens of hours of play into it. It's improved my body image significantly, plus it's just fun trying to beat your high scores. I actually went out and (ordered online) the first Dance Central just so I could import the routines for use in DC2's multiplayer.