OCaml's syntax is not what's "holding it back" in my personal opinion, but that doesn't mean it's "fine". I regularly praise it as a language (even as a former developer of the main Haskell compiler, which adopted Mixin-style modules decades after the fact) and "the syntax looks like shit" is absolutely one of the first immediate turn-offs for pretty much everyone I talk to. It's also one of my own complaints, but OCaml has a lot of good stuff too so I can put up with it.