Installed the Preview on a VM. It seems ok, but nothing to get overly excited about. Just a tweaked Windows 8.1 with a Start Menu built-in. Not bad by any means, but not currently something worth writing home about.
Also I was hoping they'd add iron out some issues, such as not being able to read the titles on dark themes (which you can on Windows 7, that's THREE Windows versions ago) and being able to customize Windows colours from white to light grey (Light sensitivity syndrome and dyslexia so this is one of my coping mechanisms) which in Windows 8.1 I've had to use registry tweaks for, again Windows 7 has these options.
Also, as if to add a new problem, the current home folder on the File Explorer makes no sense, I'd rather it shows "This PC" then the Home folder when you click on the File Explorer icon, or at least the option to choose.
It is an early build however, so fortunately there is plenty of time for these issues to be ironed out, we'll see...