OpenCart 3.x: Please use Power Reviews, which is a more powerful solution, and includes this function.
This is a very simple extension. It enables a module to show the products that have received the highest average ratings in customer reviews.
Please read documentation!
Support is at http://forum.opencart.com/viewtopic.php?f=23&t=84834
I hope you enjoy this extension. If you'd like to donate, please PayPal to email@example.com