There is certainly a right way to critique. When submitting comments, I think we must remember an important rule, often, it is not what we say but how we say it. Sometimes even a lack of words can make a critique sound sharp.
I think people must understand another very important point when doing a critique, a person's individual interpretation may not exactly coincide with that of the author of the graphic.
Good advice and encouragement is priceless.
Rupert