So I tried the windows 10 upgrade, and I have some comments.
It is absolutely terrible (imo). if you are a 7, 8, or 8.1 user, I would highly advise against downloading this upgrade. Numerous complications arose from installing the upgrade. For one, my laptop brightness was fixed on high (higher than normal, and it gave me headaches). I tried everything there is to try from 3rd party programs to restartting to even messing with the boot settings but nothing fixed it. On top of this, it took 10 minutes to boot up, ran very, very slowly, and the graphics card drivers did not seem to install correctly, resulting in very poor graphical capabilities (project 64 was averaging around 40 fps).
It's unfortunate that you had a bad experience with installing Windows 10. There is still a lot of hardware that hasn't had updated drivers for the OS and there is admittedly some driver baffonary happening on Windows Update for some people since the Windows Update drivers are older than the manufacturer drivers or incompatible with the hardware in some cases. It sounds like your laptop brightness and video problems were driver related. The startup being so slow is probably another conflict happening somewhere. While there have been a lot of success stories, stuff like this does actually happen. So yeah, I don't blame you for rolling back to Windows 8.1. I probably would have also in that case since there's only so much driver juggling I'm willing to do, especially for major devices like the video. 
But I'll go through some of your points here since I don't think everything you said is accurate.
constant stupid pop-up windows
You can disable almost all of those if they bother you.
hibernate being hidden
Hibernate is hidden, but I think you can make it show up: http://winaero.com/b...-in-windows-10/
They probably did this because they are trying to promote the fast startup a bit more and maybe feel users manually initiating hibernation is rare thanks to that. Fast startup is a pseudo hibernation since it also keeps files on the hard drive about the state of the OS to make starting up faster. It's kinda silly that full blown hibernation would be hidden for a laptop though.
if you were using classic shell 8 you won't like windows 10 start menu very much
Classic Shell works in Windows 10. I dunno if you were implying it didn't work or if you were just saying that if people felt to need to use it in 8 they wouldn't like 10, but figured I'd mention it.
Oh yeah, if you aren't running on 8.1 it will wipe out all your files I think, so keep that in mind.
I did an upgrade from Windows 7 to Windows 10 and all of my files, programs, settings for those programs, and most of my explorer settings (the ones that were still in Windows 10) were kept. It even kept my shell extensions for explorer like Link Shell Extension when I thought it was going to wipe them. About the only thing that wasn't kept was that it switched my UAC back to full annoying popup that freezes screen interaction mode and I had to turn it down since I've got some programs that would have been really annoying to use otherwise. My Windows 7 install was still pretty recent, so I didn't even bother to do a clean reset afterwards and things have been working pretty smoothly for me.
So yeah. Again, it's pretty understandable that you went back to Windows 8.1. There's still a lot of devices that just haven't gotten driver updates to work smoothly in Windows 10. This early on, you'd probably have to do some hunting to find compatible drivers depending on your laptop. It might be worth giving it a shot again a few months from now to see if Windows or your laptop manufacturer have gotten their drivers together.
Or if you're happy with 8.1, that's fine too.