I hesitate to recommend Part I of the OCaml Manual as an introduction for new users because it is so terse and dense. It describes the core language on a single HTML page. Powerful features of great consequence are covered rapidly. For example, variant types are relegated to a single section with only three example types.
I do not mean to complain about the OCaml Manual; its succinctness is a virtue. It assumes I am competent and does not waste my time. Nearly every sentence in Part I conveys vital information and should be read carefully. But people are not used to engaging with tutorials in this manner. They expect motivation (explanation of the reasoning behind various features) and hand-holding, which they can skip over or consult depending on their level of understanding. Ideally, they want to see an example that does something similar to whatever they're currently working on.
Most people actively involved in the OCaml community right now have either read the language reference (i.e., Part II) or are capable of doing so if they wanted to. Many of them have substantial background in programming language theory. But the majority of programmers cannot learn the language in this way. I think appealing to them requires a more didactic method.