personalize the rating system
I don't know if this fits the philosophy of letterboxd's rating system, but I think there will be an average overall still:
How about adding a feature to everybody's profile page (maybe with none or default settings if the user chooses to not change it) that enables you to personalize how you value the star rating with individual, editable expressions.
I think that some users rate movies more severely or more mildly than others. The personalized rating description would make it more easy and fun to classify a certain user's rating.
Let me be clear that this would be a descriptive feature only, nothing that would change the functional logic of the rating system. One could just add it to the bio on the profile page, but I think a feature for this would be more elegant and fun.
How do you think about this?