What do you mean by "ripoff"? F# is not OCaml, but it indeed is closely related. They share some syntax and basic language features like tail call optimization, records and variants or pattern matching. On the other hand F# object system is completely different from OCaml's as it needs to work with other .NET languages. F# introduces active patterns and operator overloading which is absent from OCaml. OCaml features a very sophisticated module system, which in turn is absent from F#.

In short, F# and OCaml are similar but distinct languages. Both are interesting and worth looking into, each in its own right.