A better way to do recommendations is to find readers who have rated books similarly to me and tell me what books they've rated highly that I haven't already read. This is what Netflix's Cinematch once did and it was good. It used singular value decomposition and other linear algebra techniques on a giant matrix of raters.
I don't remember ever seeing a rating system (for books or tv) that let me do fine grain rating. And if it had it, most people[citation needed] might not use it anyway. Also, how would I say that what I liked the most about a fantasy book is the magic system, for example?
I don't care HOW the recommendation is implemented, but what shows on the recommendation. For me, 'Readers also enjoyed' shows things that are sufficiently similar, and which people that I follow - friends and bloggers - gave good ratings.
The 'lists with this book' section is also good for discovering books, as the lists are user curated, and the title helps me know what's the common theme. Ie: books with cool magic systems.
A product has features in some high dimensional quality space. When you rate it, you provide information about your preference for those qualities without needing to explicitly rate them or even have a concept of what they are called.
In terms of recommending what I am already likely interested in based on my previous reads, the "Readers also enjoyed" section seems decent to me. Is that what people think sucks? I've used that a fair amount and found it to be valuable. Or is it the whole "Browse" section that's bad? I never look under there.
I use goodreads every day, but that means spending 5 mins max on it (I hop in, add a book that I heard about somewhere to my to-read list, then I hop off). And, like I alluded to in my first reply, from what I can tell this behavior also holds true for my friends. I don't think I'm an outlier, though I totally understand that people use the site differently than me and they find it wanting.