Well off the top of my head...
replyActive patterns, computation expressions, structural typing, statically resolved type parameters, explicit inlining, function composition, structural equality, custom operators and much richer generators.
type providers, units of measure, active patterns, complete type inference.
replyNot sure I would want the last thing in C#, I think having boundaries at the function signature for that.
Units of measure
replyF# units are handy, but nothing like Manifold units (Java):
replyhttps://github.com/manifold-systems/manifold/tree/master/man...