So, completely restored my SP3 to factory to get rid of my old Win10/Win8.1 dual boot. Complete pain; had to download the factory restore image from Surface support and blow everything away to get it done. That was complicated by a Microsoft system glitch that hid my SP3 registration from me, so I couldn't download the image for about two hours. Grrr. Things were fixed eventually and I was able to restore Win8.1, then I upgraded to 9926 from there.
Overall I'm liking the direction Microsoft is heading in here. But, so far, I'm having a number of issues with this build:
1. My fan is running like a jet engine, as some others have noted. I'm hoping it settles down after all of the initial install tasks are completed. Otherwise, that alone will force me back to Win8.1.
2. A number of Store apps won't install, e.g., Kindle and Stumbleupon. I get error 0x080070003 (think that's it). Not sure what the issue is there, if it's the app or Store.
3. I can't connect to my WD MyCloud Mirror NAS. Get an error about not having permissions. If I can't resolve that one, again, I'll be heading back to Win8.1.
4. The system seems generally unstable. Lots of apps just crash randomly, for example Mail when maximizing from the taskbar.
5. Playing YouTube videos crashes IE hard. I can switch to Chrome in the meantime, but I've grown accustomed to IE (believe it or not) not the least because of the nice syncing with Windows Phone. Won't force me back to Win8.1, but I'd rather it worked.
6. Live Tiles don't seem to update correctly. For example, read emails in Mail don't clear out.
So, after no using Win10 for awhile and being very hopeful for this build, I'm a bit surprised at the regression in stability and reliability. Don't know _why_ I'm surprised, because this is a pretty massive undertaking that's still in remarkably early stages for a release yet this year. But, there you have it.