Make it like a RESIDENT EVIL game or something.

At the end of the dungeon you are scored with a rating the developers think you should be at. It's up to you if you want to share the score with others if you feel embarrassed about not doing well.

S rating to E.

I think it would only encourage players to get better. To strive for that rank at the end. It would also be cool to get extra exp and gil if you score S rank or whatever.