A page that displays course and professor rankings lists based on understandable combinations of review features.
E.g. "Easiest courses", which lists the courses which require the least amount of work outside class each week and the most generous grading.
A course/professor score should take into account the number of reviews it has, and on a feature level, the standard deviation of the average feature value. The first is so that the course with a single review that says it's super easy does not trump the course with 100 reviews that say it's pretty easy. The second is to balance the first, so that a course with a few reviews but a lot of consensus is not completely upstaged by the course with a lot of reviews.
The page will probably need to be generated and cached every X minutes. Generating it will probably be pretty processor intensive, so I would delegate the task to a worker dyno to avoid hogging a web dyno every X minutes.
Let's come up with a ranking algorithm and the lists we want, along with the review features that will factor into them.