The differences aren't so minor. I could write a list, but someone has already done that:
http://en.wikipedia.org/wiki/Comparison_of_C_Sharp_and_Java
I have programmed in all three environments professionally and I know many different programming languages at least well enough to build a basic GUI.
I say that to preface what I am about to say... Java is not the worst language I have used but it's up there. I was a professional c# programmer back when it was in its 1.1 days and now I have revisited it for another professional project and it has improved to the point where I wish it was native on the Mac and on Linux without mono. It's what c++ should have been.
Edit... I have used java quite a bit and it's a terrible language.