They really diverge when it comes to more advanced language features. I make heavy use of functors in my code and my (possibly mistaken) understanding is that F# simply doesn't support them. Ditto for first-class modules, polymorphic variants, GADTs, and OCaml's object system. Of course, in exchange for a wimpier core, F# gives you a lot of convenient polish and proper support for parallelism & concurrency.
ML functors aren't the same thing as the functors or applicative functors I often blog about. Difference explained here: http://stackoverflow.com/questions/2030863/in-functional-pro...
ML functors are like parameterized modules. F# doesn't have parameterized modules, but has parameterized classes, which work quite similarly. Classes/objects can also be used as first-class modules.
What .NET lacks (therefore also F#) is type constructor abstraction, which means you can't generically express the concept of a (Haskell) functor, applicative functor, monad, etc.
My understanding is the same. I, like you, haven't followed F# since it diverged so much in development, but it's understandable that those features would be in-commensurable with how it interoperates with the .NET framework.
