If you were previously in the Beta version of the game and the Google play store says "(Beta)" underneath the name of the app, you will have to un-enroll yourself in the beta program to leave reivews for the game on the google play store.  If you go to the Google Play store page, scroll down from the top of the store page to the App Support sction, just below that you should see "You're a beta tester" at the bottom of this section, select Leave and then confirm you want to leave. After the confirmation it will take about 30 minutes or so to successfully un-enroll so close the Google Play store and then relaunch after 30 minutes and you will see the normal store page.