I need to give ReasonML another shot. It's been a few years, but at the time it really only seemed to work if you were targeting BuckleScript and even then you had to write a bunch of Makefiles and jump through other weird hoops. Beyond that, it suffered from some other OCaml issues--multiple "standard" libraries, different packages using different async libraries, some gratuitously abstract libraries, etc.

I'm really hoping it breaks into the mainstream such that it gets the investment that other mainstream languages get (hopefully said investment will smooth out these rough edges).