Ratings is such a tough thing to regulate. With the ability to adjust the weight of each category in the rating, it reduces how comparable each rating is to another. For this reason, I've always left the weighting as the Pinside default. I've rated about 60 games now, and all fall in the 6.8-9.4 range. Each time I rate a game, I put in my full honest gut feeling across the board. If the result is lower or higher than I think it realistically is, then I will adjust as necessary.
I'm guessing a lot of people don't put much nuance into these ratings. Just like so many things in life, the very vocal fan boys and haters end up sticking out because they are putting ratings that really are far from realistic.