Currently the only way to create an account is through GitHub login (we're going to add more options in the future). That means in order to write a review you have to log in with GitHub.
Behind the scenes, text reviews do not show immediately, we go over them and approve them manually, to verify there's not bad behavior, spam, offensive content, etc.
We plan on approving each text review ourselves manually until we're stretched too thin and this plan doesn't scale anymore.