there isn't actually a ratings system :)
the recommendations that are shown are based on votes, and you can see the reason for those votes by clicking the flashing talking bubble icon. they are sorted by number of votes as well. there isn't actually anywhere that people can vote on a RATING for each series (as in, voting trigun an 8). or are you getting at something im not understanding?
there are also reviews located at http://www.anime-planet.com/reviews/
, but those ratings are a bit different ;) .. you can sort each reviewers' votes by score, i dont think ive done that for ALL reviews, though i could do that if people are interested