Starting with build 0.4.8-dev-655-g63a3a2c, ReactOS has first support for NT6+ applications (aka programs written for Windows Vista, Windows 7, etc.). Please retest such applications under ReactOS!
As newer Windows APIs are still missing in ReactOS, I would be surprised if a high number of NT6+ applications suddenly works. However, many applications may just be compiled by a new Visual Studio without using any modern APIs. They could work now.
My "Hello World" compiled by VS 2017 v141 toolchain printed many messages about missing apiset DLLs in the debug log, but otherwise works well. So the next step should obviously be finishing and integrating Mark's work on the apiset DLLs in https://github.com/learn-more/reactos/commits/apisets But interestingly, the build produced by the v141_xp toolchain also looks for these apiset DLLs. Therefore, it would be possible that an application expects a full NT6 system when finding them. Consequently, application compatibility could be compromised if we just dump all apiset DLLs into ReactOS, applications now expect NT6, but the OS continues to behave like NT5 by default.
This is why I suggest detecting an NT6+ application in ntdll to have it auto-apply a shim that lets ReactOS behave like an NT6 OS. The apiset DLLs should only be available in this mode, but not for the NT5 personality of ReactOS. Let's not import the apisets before the ntdll shim work is done in order to preserve our existing application compatibility.