One common critique is that in the toplevel (REPL) you must terminate your inputs by ;; and sometimes you will see code that puts ;; between function definitions too.

Also, nesting pattern matches is a bit ugly:

    match x with
    | Foo y ->
      match y with
      | Yes -> ok ()
      | No  -> not_ok ()
    | Bar z -> whatever()

does not work, it must be:

    match x with
    | Foo y ->
      begin match y with
      | Yes -> ok ()
      | No  -> not_ok ()
      end
    | Bar z -> whatever()

which is not a big deal but surprisingly easy to forget.

Some people would also really like to write

    let x = foo
    let y = bar
    x + y

but it has to be

    let x = foo in
    let y = bar in
    x + y

and those many "in"s accumulate.

A bunch of these things look a lot cleaner in Haskell. Although it does it by being indentation-sensitive, which other people love hating.