Direct3D can be a good API, but Microsoft played dirty to make it succeed, and that matters.

If you were around those days, Microsoft said that OpenGL on Windows was going to be put behind a backward compatibility layer, with a performance penalty. All developers got scared and switched to Direct3D.

For this reason, I don't care if Direct3D is a good API. Direct3D is the reason of why most games cannot be ported into other operating systems or are forced to run on WINE (with issues and performance penalty), and is also the reason of why Windows has a larger market share than it should.

I really hope Vulkan takes off and replaces Direct3D for most uses.