As others have said, F# interesting language features are computation expressions, active patterns, units and type-providers. The library, platforms and ecosystem benefits are gravy. Though subjective, the syntax is clean too, being somewhere between an ML and Python.

Something that no one has mentioned yet is that F# is now among the fastest functional first programming languages. At least according to (take with a grain of salt) benchmarks like [1] and https://www.techempower.com/benchmarks/

[1] https://benchmarksgame-team.pages.debian.net/benchmarksgame/...