There are book lists on the page for you to scroll through, and on the left, there are spectrums for you to choose–happy/sad, beautiful/disgusting, gentle/violent. By changing the settings on these, the books on the lists will change. The picture below shows the results.
I can see myself using this in class to help readers who have very specific reading preferences find their next book to read. I have to admit, I spent almost an hour fiddling around with the different settings and seeing the results. Check it out and see what your next book might be!