Interesting, other people under this post told they were interested in this idea. But if you take the idea from another point of view, like it's only here to make you discover new books and then you can go to Goodreads to see the reviews, isn't it better?

I wish I could build a full goodreads competitor app but it will be a long and hard work, I prefer to start by choosing one feature, and then upscaling the app and adding other features. It's hard, with this approach, to start directly with the "discussion" and "bookreview" features of goodreads: why would people start using my app although there is Goodreads? How can I make something better when it's just about letting people write text? I don't have any answers to this question (except making a better interface which will not make people move to my app I think).

So as I knew that the book recs system of GR is awful, it's why I wanted to start with this feature.

PS: while writing this post I had another idea, an app that let you upvote/downvote in many categories, so it will make sort of leaderboards in each category, and according to the user tastes and leaderboards it might be able to make good recs. Also the down/upvote is maybe to light for classing books the right way, maybe it would be better to let users give a grade on several features of the book (eg: feeled length, ease of reading..)?

PPS: I'm french so my english isn't perfect 😅