For me personally, there are 3 main reasons that I have been super excited about .Net core:
1. It is C#, in my opinion the best statically typed language. The easiest way I have described it to other folks is it is Java++. Combine it with really good intelligence, and it is like the code “flows out of you”. Part of the reason for that is the effort put into the language itself (getters/setters, lambda functions, etc), but equally and possibly more important is the support of Microsoft, so this is a language/toolset that is being used daily to make itself better. (In my opinion this is why Jetbrains is so good, the developers use their own tools constantly).
2. It is cross platform from the ground up. I can’t understate how great it is to have an alternative to java
3. Rosleyn: being able to compile and potentially be as fast as C++
Just my 2 cents