var foo = [1,2,3];
Add on switch expressions, primary ctors, first class functions, no ceremony in Program.cs anymore... it's hard to get more terse and expressive unless you want lots of chained single symbol operators (look at F#).
void myFunc(List<int>){}
myFunc([1,2,3]);
The expression sytanx can infer the type from the caller syntax so you can just inline the array declaration.
The downside of all this is that the only people that know how awesome C# is are people who are already doing C#. Growing the pot and trying to convince people to give it a go in its modern (post dotnet 5/"core") iteration is like pulling teeth. Everyone assumes nothing has changed since like C# 2, and given the fact it's a "boring" language that doesn't have Hacker Hype behind it, people just ignore it.
Every week you have people on HN wishing for something that does exactly what C# does but don't want to give it a shot or admit that C# is _actually_ an incredible language and toolset that does exactly what they want (and more).
They have support for these features, but they require some ceremony to use (like wrapping function arguments in a Callable), which increases friction, signal to noise ratio, and decreases the expressiveness that I want.
I just want to write what I want without having to think too much about how the language wants me to write it. Go is good for that. JS too, but has a lot of historical cruft.