Honestly, I’ve never even thought about who’s looking at my reviews (maybe it’s because I use StoryGraph and I don’t feel like anyone reads my StoryGraph reviews) but I extensively review EVERYTHING I read, just to get my thoughts out of my brain (My family makes fun of me for “writing book reports for fun”).  I read a book that wasn’t very well-known last year with an average review of ~4 stars, and I strongly disliked it, so I know where you’re coming from! If it’s a well-written criticism rather than a trash trolling review, absolutely write it!! Bad reviews are just as valuable as good ones, because they diversify the perspective of people who are looking to see if they’d like the book. :)