I can absolutely understand that it makes sense to have a much more fine-grained average, but personally I struggle to give meaningful ratings beyond the four I mentioned.
That said perhaps multiple binary dimensions would be better. Good story yes/no, interesting/unique premise yes/no, overall good acting yes/no, good cinematography yes/no etc etc.
I was interrupted, so when I picked up my brain continued with movie recommendation mode, I watch more movies than read books, but the binary multi-dimensional rating could of course be applied to books as well.
That said perhaps multiple binary dimensions would be better. Good story yes/no, interesting/unique premise yes/no, overall good acting yes/no, good cinematography yes/no etc etc.