I thought https://book.sv was pretty good. It was on HN recently: https://news.ycombinator.com/item?id=45825733. When I inputted 5 books I liked, the recommendations were a combination of:

1. books I had already read and enjoyed before

2. books that were already on my list (either from friends or other recommendations)

3. books I hadn't heard of

That said, I haven't read a book from #3 yet, so I can't fully vouch for it, but #1 and #2 are positive signals to me.