Yes C# is an improvement over Java. But, that isnt saying much with the plethora of cutting edge languages available today.

I still prefer Java, because C# is limited to the Windows environment,Mono isn't much help yet, and that is a huge limitation for me. Especially because Windows is not conducive to any serious systems programming - its ugly.

Another reason in favour of Java is the better open-source eco-system, more libraries and much more mature stuff.

C# has had the benefit that all new products/techs have - it leapfrogged.