F# isn't "just a[n] MS implementation of OCaml, with a few small differences". F# did start out as an OCaml port for .NET, but the language has grown organically from there, especially since the first public, supported release (v2.0, in VS2010).

The foremost difference is the ability to easily and closely interoperate with existing .NET code; this sounds very simple, but it's very tricky to get it right, and in fact this is widely considered to be a major strength of F#.

F# also has computation expressions (like monads in Haskell), sequence/list/array comprehensions, type providers (for strongly-typed data access), and built-in async support. Not to mention, since F# runs on the CLR, it has a well-tuned, high-quality, multicore garbage collector at it's disposal.

I know some of the folks from OCaml Labs, and I have nothing against OCaml. I just want to dispel the notion that there are no differences between OCaml and F#.