Not to imply this functionality is complex, but really the most important thing for me are the lists:

I _love_ that I can take a book I enjoyed, see it's on a list of "Best Magic Systems", and note what was rated even better for its magic system

A simple method of discovery for me

https://www.goodreads.com/list/show/871.Most_Interesting_Mag...

https://www.goodreads.com/list/show/8497.Aliens_First_Contac...