Is this 'Reason' just slightly modified Ocaml to look a bit more like JavaScript? I don't get it.
seems like a more verbose ocaml for the javascript generation
Yes. Facebook decided to make an alternative syntax for OCaml for JavaScript users. Personally, I can't get behind it because it seems to be fragmenting OCaml (this article references OCaml in the title, but doesn't apply to actual OCaml code, making finding actual documentation much more difficult). At the same time, it seems like wasted effort when most of the process of adapting to OCaml involves learning the semantics and paradigm rather than the syntax.