I now have Windows 10 on my laptop.
Took 2 tries, 1st one it failed near the end for no reason but it properly restored Windows 8.1.
Soooo I tried again but with ethernet connected not wifi (just because) and it installed fine. Immediately went to Windows update and it already had an update waiting. Right now it is doing the restart after update and I am waiting so see if it works after that! Certainly the update process is very slow compared to W7 or W8
So I'd say it acts like a service pack so far rather than a brand new OS...but I suppose at this point that is what it is.