The only reason to post on a fic shouldn't just be to criticize. What kind of forum would this be if the only posts you ever read were negative? What about the great fics, the ones that are genuinely excellent? They would literally get very few to no reviews, while mediocre fics would get mountains of reviews.

As for spam reviews, the rules already prohibit those, but that's hardly the point. I've got to agree, there is nothing inherently wrong with the review system right now.