I like the idea of justifying ratings, but that can still be gamed, unless justifying ratings is one of their explicit performance objectives. At one of my jobs, managers had to provide more justification for the very highest and very highest ratings. So my boss told me that I deserved the highest rating, but he didn't want to provide the extra justification, so he gave me the next highest. And he confided - unprofessionally - that he knew (as we all did) that someone else in the group deserved the very lowest rating. But again, he didn't want to do the extra work, so he gave him the next to the lowest rating.