[V-2]

I don't want to argue over what "enormously" means, but LINQ is a big boost for productivity, and it's not just LINQ-to-Objects, but also LINQ to SQL, and extensibility thanks to expression trees.

And LINQ isn't an isolated example. There's an asynchronous solution for asynchronous programming built in the language (async/await since C# 5.0).

There's reactive programming - RxJava is most popular these days, and most major languages have their RX thing now, but it was in the .NET world where Reactive Extensions saw the daylight for the first time.

Or MVVM (10 years later, Google began introducing it to Android, though it's not production-ready yet).