I've ultimately bounced off most review sites I've tried because their algorithms and feedback structures just don't vibe with how I think about books, but I've found this rubric really helpful to me when I was trying to come up with a star rating. It's designed for rating movies, but that breakdown of things like "under what circumstances would I buy or re-watch/re-read this" and "would I only rec this to someone who likes this sort of thing or to someone who usually doesn't like the genre" was helpful to me.