The Rate My Professors extension adds a Rate My Professors icon to your Chrome browser. When you click on the icon, you can view the professors' ratings and reviews for each class they teach. 

These include:

A student's overall rating for that course, and a ranking in comparison to other professors. 

A level of difficulty, if the student would take the professor's course again. This information is accessible through a popup that will appear when you mouse over the professor's icon.

The most recent reviews. These appear at the bottom of the popup when you click on the icon.