I’d like a build system that didn’t rely on make, as that can be tricky to obtain on Windows 
Having said that, I’d agree with “better documented” as a goal. It’s tricky to remember what the various .bat files involved in a PC build (and running the tests) do, and what their parameters are. And what knowledge I do have there isn’t transferrable at all to the Unix build system. So “a single build system for all platforms” is important to me as well.
Also, a Windows-specific one, but the build system should automatically locate an installed compiler. Having to run the build from a “Visual Studio command prompt” would wreak havoc with my workflow (as the VS prompt starts up a whole new terminal window using a different shell).