I recently went ahead upgraded to Windows 10 when I upgraded my PC, and other than the fact that I had to install Windows 3 times in order to get a clean install of W10*, there haven't been a single issue for me. The new start menu is kinda meh, but I mostly just type the name of whatever I want to run anyway, rather than navigate it by hand, so I rarely even notice it.
If you are unsure, and have a spare external HD available (that is big enough), then you could probably make a full disk image before installing, so that you can easily revert back to whatever you were running previously. Unfortunately, I can't give any advice on how to accomplish that other than booting into Linux and just using 'ntfsprogs'. Perhaps somebody else in this thread can recommend some tools.
* I had accidentally deleted the boot partition for my W7 installation previously, so I had to reinstall that first, then do an upgrade to get a W10 key, and then I could do a clean install.