Not really. We've tried running several C# programs on mono, and as of a few months ago, the effort to port them so they will work on mono was pretty intense, and the performance was lacking.
C# (especially when developed in VS) is a nice language and environment, but cross-platform is not one of it's strengths.
I am sure I would have similar issues with Java on *nix because of my lack of experience with both. Cross-platform is definitely a major C# strength at least in the mobile space given the power of Xamarin tool chain. Android and iOS do matter and they are not Windows.
C# (especially when developed in VS) is a nice language and environment, but cross-platform is not one of it's strengths.