Goodreads recommendations are decent; I can often find at least one related book I’ll want to read from a book I’ve read. My problem is exactly the opposite as yours: I can’t read books as fast as my backlog grows! Most of my recommendations come from Goodreads, discussions on HN, or one or two reader friends who make recommendations I like.

Oftentimes the books I read cover only part of a very large topic, and this leads me to seek out books covering the rest; for instance, I do not expect my interests in political/societal structure and economics will ever stop yielding new books to read.