The Windows Update driver thing was one thing fixed in 1511. I did notice the original build was upgrading my drivers for me despite the settings, but they reworked the control panel function for that and it does seem to be behaving itself now.
I have also never run into any random programs getting loaded onto my computer. Sure, there is always the stuff that comes with Windows initially (and they do have a few extra pieces of junk included out of the box now), but nothing since then. Also I've never seen a single ad in Windows anywhere.
The UI is a personal preference. I agree it is a bit plain, but I wouldn't quite call it ugly IMO. Its just "OK" to me. I am hoping for some 3rd party skins and themes at some point so I can customize a bit more.
Drivers I can see a sticking point, but blame nVidia etc for that one. Side note, I haven't noticed any missing features in my Radeon driver package.
The "Bipolar setting/control panel system" as you called it is a bit annoying and I haven't figured out where everything is quite yet.
I also haven't messed with high DPI scaling since I just run 1920x1080 and the regular DPI is perfectly fine for me. If I had a 4k display maybe that would be different, but I've always found DPI scaling to be mediocre at best in the past so I guess I wouldn't have expected much there.
I've not tried Win10 on old hardware, unless my 2600k is considered old.