One of the features I like about Netflix is that it recommends movies you'll love. The more movies you rate, the more accurate these suggestions are. You should browse Netflix and rate every movie you've ever seen, not just the ones you've rented from Netflix. This really makes a difference.
The red star ratings you see on the Netflix site are actually predictions of what you would like, based on other users' opinions. If you rate more movies you have seen, those stars will start to reflect your opinion more than anyone else's.
I have rated 3,246 titles on Netflix.com. It's possible that I've seen more than that, I just can't remember them all. As a result, there are 347 movies that Netflix expects me to love. Does that number seem low to you? Or is it about right?
Back before the Netflix Prize was awarded, I had very few recommendations from Netflix. Less than a hundred. I think my taste in movies is so personal and eccentric, that it's hard to predict what I will love. Even the Netflix algorithm predicts only four stars for "movies you'll love." Shouldn't it predict you'll give FIVE stars to movies you will love? I guess it's because my taste is so idiosyncratic.