I realize this may be considered off topic here, as I'm asking about the Win 8 RTM available on MSDN subscriptions.
What is the edition? I installed the Win 8 x64 available, but all it says when I look at System in Control Panel is "Windows 8". No edition mentioned.
When I try to find Gadgets (in Win 8 RP, right click on desktop, select Gadgets), the option is not there in the RTM.

It depends upon which product key you requested. There is a standard Windows 8 and a Windows 8 Pro. Go back to the MSDN site and click on the request key button. You should have the option (presumably depending upon subscription) to request a key for Windows 8 and/or Windows 8 Pro.
Incidentally there are no gadgets on the Pro version either. I'm sure Microsoft had a problem with Gadgets (virus or something) and requested users to disable them. I would imagine, although I might be wrong, that they have been removed from Windows 8.