Speaking as someone who has been doing C# for over 15 years, and still professionally, but who uses F# almost exclusively in my private projects, the biggest th

Speaking as someone who has been doing C# for over 15 years, and still professionally, but who uses F# almost exclusively in my private projects, the biggest things are: - discriminated unions. DU types don't exist in C# or lots of other languages, and change the way you program - complex match expressions (fortunately coming in C# 8) - value tuples (thankfully arrived in c# 7) - the pipe operator and partial application (another thing that changes the way you program) - super implicit typing (its to var what var was to explicit typing) - and its use of option/result types, along with compiler enforcement of all conditions. Before I picked up F# properly, I looked at it as fancy but overhyped. But then, its a bit of a plato's cave type of thing: you don't know why `type A = B of int | C of string * bool` is awesome until you have used it a bunch of times.