I am currently looking for a 3D engine in C#. I have no preference between an OpenGL or DirectX one. After some tests, i think Brume is a good engine with nice features. My choice is not definitive at this time, i have to test another engines.
If i can give you an advice on your engine, before added new cool features, try to make an effort on documentation and refactor some parts because some classes are obvious and redundant (or maybe i don't understand the philosophy of the engine ).