I always say the only praise that counts is from fellow musicians.
By the same token, criticism from musicians is worth listening to.
If you are going to criticise, keep it to one or two clear points. A friend asked me what I thought of his band who supported us the weekend before last. I said basically you were far too loud, especially one guitarist - I couldn't hear your bass. He said "yes, he soundchecks at sensible volume ten turns it up when we start".