Comment by WorldMaker

Favorite recent language feature is a big investment in C# pattern matching. It's a big feature from the functional programming world rare to see in "Enterprise" languages.

Favorite recent runtime feature is all the cool low level stuff opened up by Span<T> (and Memory<T>). It has a similarity to Rust borrowing, but well integrated into the CLR's existing type system. It has opened all sorts of performance code possibilities that is still memory-safe/type-safe with fewer needs for falling back to "unsafe" operations. This is not just exciting because it is an interesting playground if you like low-level programming, but also because it has been a performance flood lifting all boats in the .NET ecosystem. A lot of code over the last few years has gotten easy performance boosts by just recompiling (because the compilers were taught to prefer Span/Memory overloads when they get added; no change to C# or F# code, just the compiler picking a new performance path).