......the guideline for etiquette on the forum is "how would you act if meeting someone for the first time at a cocktail party". One can be objective, factual, respectful, knowledgable etc etc and it does not need to cross the line to rudeness of any kind. Of course, that does not mean a free-for-all to express personal opinions when such personal opinions are purely subjective and potentially offensive.
Objective and constructive evaluation is great.....personal truths applied as if they are facts are not.