Short Version? You should be safe to upgrade, and in most cases you'll notice a decent speed boost. It's quite a nice OS to use!
FWIW, there are things Win8 greatly improved on, especially speed (even on older hardware.) File Copying and program performance are much faster, and since Win10 shares much of the underlying architecture, it also inherited the performance increases. (While many new features have been added, the main differences are in presentation: Windows 10 expands on win8's modern aesthetic, but makes it infinitely more palatable to desktop users.) Because of the shared foundation, any fixes or workarounds for Win8 can be easily applied to win10.
However, like I said, I never had any compatibility issues appear while using win10, (or win8, for that matter) and I may be biased in that regard. I don't expect any major incompatibilities to appear in the next few months, and at the risk of generalizing too broadly, any program that supported windows 7 can work on windows 8, and therefore will work on windows 10.