New in the upcoming release[1] will be the ability to run C# files as if they were scripts[2], ie without an explicit build step. Should lower the barrier to just fooling around.
I also like how they've gone away from the "everything must be an object" style ala Java, and allow top-level statements so it reads more like C/C++. It's just sugar, but for smaller programs that really makes a difference IMHO.
[1]: https://news.ycombinator.com/item?id=44699174
[2]: https://devblogs.microsoft.com/dotnet/announcing-dotnet-run-...