At this stage, its just Vista, but with some additional features. I think this is what this release is about, purely to show what will be included in Windows 7.
The 'Show Desktop' icon has been replaced with a button that sits to the right of the clock. This is good, as I think the Show Desktop button is imperritive in today's desktop needs.
It has new themes and the control panel looks a bit different, but right now, its no different to Vista.
It may have been running on the 7 kernel, but I don't know. The 7 kernel is said to be very small by todays standards. I saw a video with a guy from Microsoft giving a seminar and said it was about 40mb, but still not as small as he would like it.