Previously it added a lot of stuff on its own like async, etc. which was cool but also resulted in compatibility issues when c# later added similar features.

Now the f# developers are very concerned with compatibility but it basically means that f# can't get new features until c# already has them. It's also limited by the runtime which is designed around c#.

For example, it doesn't support type classes because (among other reasons) that might end up being incompatible with future c# type-class like features several years down the line.

It's also hard to learn f# unless you already know some ocaml/haskell.

ocaml has failed to catch on that much so far but I think it does have potential, and adding multicore support/effects is pretty promising.

On the other hand the fragmentation with stuff like reason/rescript is pretty dumb.