If you already know Java, learning C# should be piece of cake.
I've heard that argument before and even given it myself.
Having gone through the pain of switching platforms I can say: lies and shenanigans. The LANGUAGE is a piece of cake, you learn that in under a week. And then it begins, months of hard effort. It begins with something that is easy for some but hard for most: to change your mindset and open yourself to all that is new in stead of rebelling against it. And then you can start: learn the little differences, the conventions of the platforms, to figure out where to find and how to look for information, to cram the basic prerequisite API knowledge into your brain (to actually be productive in stead of having to go to the net or a book for each line of code you write) and to cope with the tooling and deployment.
Noooo, its very difficult indeed. Perhaps "difficult" is not the right word - time consuming.
Actually, once you know one language good, other languages themselves will be very simple to work with, not just limited to cousin langauges like Java and C# as I implied/said earlier. But as you say, the libraries, conventions, tools and actually being productive is much more time-consuming and more or less difficult.
