F# is a hybrid language just as C# is. Just a different flavour of the mix.
Yes a longer answer is that it is "functional first" just like C# is "OO first". It's safe to say that f# is much closer to ML than Java tough, so it's very much a functional language in a way that C# is not.
So you'll want it if you want a functional language and you want to use the .NET platform.
Does that answer your question?