I quite like it for finding books in the same series. For example, this finds all the ringworld[0] books, but the other site mentioned in this thread does not [1].

EDIT, but looks like LibraryThing, also mentioned here, does![2]

[0] https://www.goodreads.com/search?q=ringworld&qid=DjSO9UZu2o

[1] https://www.worldswithoutend.com/searchwwe.asp?st=ringworld

[2] https://www.librarything.com/nseries/703/Ringworld