> That seems pretty hard to read at a glance, and easy to mistype as a definition.

YMMV but let expressions are one of the nice things about OCaml - the syntax is very clean in a way other languages aren't. Yes, the OCaml syntax has some warts, but let bindings aren't one of them.

It's also quite elegant if you consider how multi-argument let can be decomposed into repeated function application, and how that naturally leads to features like currying.

> Also, you need to end the declaration with `in`?

Not if it's a top level declaration.

It might make more sense if you think of the `in` as a scope operator, eg `let x = v in expr` makes `x` available in `expr`.

> Then, semicolons...

Single semicolons are syntactic sugar for unit return values. Eg,

  print_string "abc";

  let () = print_string "abc" in