It has a tendency to recommend books in the same series as are input (putting aside that if I like a book in a series I've likely already read the series).
It did suggest Murderbot Diaries (not on the input but a series I have read and did like) and an Adrian Tchaikovsky I hadn't read :).
It's explicitly trained to predict the next book read in a sequence, which is why you get that behavior. There's probably a better way for me to handle it rather than having 5 books from the same series tend towards the top though.
If you have the data to know the other books in a series maybe split the results so you have "books in series" in one column and "books not in a series mentioned" in the other but other than that it did a better job than Kindle recommendations which are often hilariously off the mark.
Yeah the hardest problem for recommendation systems is to find non-Star Wars books which are like some specific Star Wars books and unlike some other Star Wars books. I would say it's AGI-complete ;)
It did suggest Murderbot Diaries (not on the input but a series I have read and did like) and an Adrian Tchaikovsky I hadn't read :).