Actually the rule "facts only" would not really work for this as the reviews will necessarily be opinionated. So it would be more like, in the positive review "The chainsaw effect is really cool" and in the negative review someone else would write "The chainsaw effect gets really boring after a while".

As for vandalism, I agree that this could be a huge problem, however Wikipedia has similar problems for contentious topics. I guess whats needed are 1) a passionate community 2) clear rules what is acceptable and what isnt.