There's a great essay called "Critique Group Dysfunction" by Hope Vestergaard in the 2005 Children's Writers and Illustrators Market that sums up the situation you're facing very well.
I tried to find it on the web a few months ago, to post it here, but it's not yet up on the boards.
In the essay she lists out the types of people in critique groups and lists their strengths and weaknesses, as well as how to work with them.
They include the Bulldozer, the Cheerleader/Gusher, Contrary Mary, the Drill Sergeant/Chairman of the Board, the Green-Eyed Monster (read as envy), the Hog/Center of the Universe, the Mother's Hen, the Mouse, the Battleaxe, the Star Pupil, the Stickler, and the Dreamer.
She also has a page on "Giving Good Feedback," which splits the criticism between Big Picture - characters, plot, structure, freshness, and theme, and Little Picture - mechanics, literary devices, character development, pov, voice, and authenticity.
Worth checking out, if even in a bookstore.