I've now got three machines upgraded to Windows 10: a laptop, a tablet, and my primary desktop. I must say that the process was painless, except for two things I've listed below, and everything works as well as it ever did. This includes not only all of the imaging software (CS6, LR6, on1, DxO, even some old Corel stuff) but also a variety of synthesizers and samplers.
The UI is different from Windows 7 and Windows 8, but it is, to my mind, much closer to Windows 7 than to 8. It feels more like "home" to me, and I can adapt to the changes.
I had two issues, and both on the desktop. First, I got the blue screen of death because of issues with my SSDs. BTW, the Windows 10 BSOD is much prettier than the Windows 7. Now I'd had this problem with Windows 7, and it was a known issue with Asus motherboards and Marvell chipsets/drivers. I had instituted a work-around for Windows 7, but the upgrade broke that. However, I was finally able to get the Windows-hosted BIOS upgrade program to work--it had never worked correctly under Windows 7--and that finally fixed the problem permanently. The other issue was a problem with a Focusrite USB sound interface. The beta driver from Focusrite -- NOT the lens tuning software, BTW -- fixed that issue.
All in all, I must say that after some time using Windows 10 I'm pleased. Yeah, I've gone in an uninstalled a few added things, such as feeds about sports or money, but I've not found the added bits to be that offensive.
Tom