I think that statement "harsh criticism helps writers" is a load of shit for two reasons:
- It reflects poorly on you; at best, you'll seem arrogant. At worst, you'll appear outright rude.
- People won't listen to you because they don't like you.
One other thing; I've seen some people do reviews in an MST3K format. Do not do this unless you get permission from the author. The reason is that MST3K's hare minimally helpful and they often come across as rather mean-spirited.