F# is indeed an ML-family language, but at this point it doesn't have all that much in common with OCaml specifically: it doesn't have the latter's structurally typed object model with inferred row-polymorphic types, nor its extremely powerful module system, not even many convenience features like open variants.
F# has plenty of features that OCaml doesn't have like proper cross-platform support, proper deployment, active patterns, units of measure, computation expressions, type providers, interfaces on unions and records, etc. F# is probably faster as well and definitely has a larger ecosystem through .NET.
