Valid Email required?

All of the form fields, with the exception of the rating itself are optionally displayed and optionally required. In the dashboard of the plugin, under the options tag you can simply remove the requirement of the email field.
As seen here
This also goes for the admin email for notifications, you can both uncheck the option to send emails to the admin when a review is submitted and you can simply leave the text field blank. Like so

Please let me know if this is not working for you.