Reason is a js like syntax for ocaml, semantically they're identical. Similar to coffeescript and JavaScript, except ocaml has really good support for this kind of stuff
It replaces a lot of the idiosyncratic bits of OCaml's syntax with things that feel more appropriate if you're comfortable with other modern languages.
A quick example is tuple types. OCaml declares tuple types as int * int, which makes total sense if you know that tuples are a product type. However, you actually create tuples using commas. Reason throws away the connection to theory and uses the same syntax for types (int, int) and creating values of that type (3, 7).
I only saw rather simple typing examples, which didn't seem much different from what TypeScript can do.
On the other hand I read often that ocaml doesn't have runtime errors, which I certainly get with TypeScript.
Of course the rest of the book is a great read too if you're so inclined.