Let's start by acknowledging that this is not a review. There are numerous reviews of the Xbox One and the new Kinect, therefore I will save us all the time of running through the specs. This is just a few bits of information and mild anecdotes to help you make an informed decision.
The new Kinect that comes with the Xbox One is about twice as tall as its predecessor, but the height is worth it. The original Kinect required a shockingly large amount of space. The new Kinect allows playing in a much smaller area, significantly closer to the sensor and the TV. With that comes the warning that the Kinect can see everything. That person in their underwear walking 15 feet off to the side of you will be plainly visible to the relatives you are Skyping with.
The face recognition is neat and indescribably creepy. I sit down in front of the console and it logs me in using my face. If Kevin walks by in the far corner for just a split second, the Kinect chirps in with "Hi, Kevin!". I was testing out a game under Kevin's profile, and the Kinect wouldn't let me. It kept seeing my face and the IR sensors of the controller and kept automatically switching to my profile. Not until Kevin was standing behind me and the IR censors were blocked by a pillow did the console let me use his tag. My Kinect loves Kevin.
When it comes to dancing and movement, the new Kinect is hugely improved. I was playing a Zumba game and that thing picked up all the head flicks and hip shakes I could muster. Everything matches pretty well and there is longer any of the distortion when identifying body parts.
If you acquire the Kinect, I highly recommend you turn the microphone off. There are numerous times when someone else is having a conversation in the room and they use the word "Xbox" in a sentence, and Kinect takes that as a cue to start listening. When I was playing Call of Duty, about once per match someone would start yelling into their mic "Xbox: Stop Listening". This thing is desperate for attention.
If you used the Kinect a lot before, then the new one will be amazing. If you thought it was clumsy, find a friend that has one and try it out. If you absolutely despise motion control, this won't change your mind. But above all else, remember that Kinect is watching and listening. If this thing isn't the first step towards a real life Hal 9000, I don't know what is.