At 10 AM yesterday everyone lost the ability to receive reviews in Google local maps. The Google team is hard at work and say they will have the reviews back up and running soon. As of this morning I was still not able to leave a review. We may see the fix roll out or come out all at once depending on what the technical difficulties.
You can read more over at: http://searchengineland.com/google-working-fix-ability-leave-local-reviews-google-maps-280822