I think a hello world example is insufficient. I would like to see some more code examples, especially some that are useful in the real world for building websites. It doesn't have to be a fully functional hacker news clone in Grain, but it should definitely be a little bit more than hello world.
It isn't only insufficient by far, it's the only complete code example. There's as good as nothing else. The chapter on control structures isn't even there. There are some cryptic remarks on mutation, but that's it.