I would hate to be forced to leave a review. I buy resources because I'm trying to save time. To make someone leave a review for something they've paid for would, I believe, results in a lot of negative comments. Having to leave a star rating for something you've downloaded for free however would be good. My British Science Week lesson has been downloaded over 1000 time with one review. I do know that I rarely leave reviews though, but would do if it were easier.