C# 4 did bring forward the covariance/contravariance feature that's been in the CLR since v2, yes. And they did add dynamic, which was the big major feature of v4.
Better expression trees, as I understand, aren't accessible from C#. That is, the C# compiler doesn't allow you to write arbitrary code as an expression. What shipped was the DLR-based expression trees, which are more flexible, but require a cumbersome API. So that's not really a feature. (Correct me if I'm wrong; I haven't used C# extensively since 3.0 as I moved to F# for .NET tasks.)
Optional parameters were a mistake to leave out of the original spec. MS insisted that providing a ton of method overloads was a more elegant approach, for some insane reason. And at any rate, the C# implementation C# is the same, lame, VB/C-style callsite embedded optional parameters, which hampers their usefulness (but it's still much better than overloads!).
Perhaps I have unrealistic expectations from C#, as I certainly don't appreciate the effort required to design a language for such widespread use.
Better expression trees, as I understand, aren't accessible from C#. That is, the C# compiler doesn't allow you to write arbitrary code as an expression. What shipped was the DLR-based expression trees, which are more flexible, but require a cumbersome API. So that's not really a feature. (Correct me if I'm wrong; I haven't used C# extensively since 3.0 as I moved to F# for .NET tasks.)
Optional parameters were a mistake to leave out of the original spec. MS insisted that providing a ton of method overloads was a more elegant approach, for some insane reason. And at any rate, the C# implementation C# is the same, lame, VB/C-style callsite embedded optional parameters, which hampers their usefulness (but it's still much better than overloads!).
Perhaps I have unrealistic expectations from C#, as I certainly don't appreciate the effort required to design a language for such widespread use.