I joined an online critique group a few days ago, my first foray into this area. I've always been wary of such things, partly because I'm not a natural joiner and few of the group forays I've previously made proved worth the time they consumed. (I find writing time precious and anything that competes with it has to pass stern tests)
I made my first critique too quickly, I should've read more of the previous crits first, and, because this was the writer's most obvious weakness, I chose to "show" rather than tell.
It was not well received and I wondered initially if it were worth the effort I'd put into it..
My second crit was more cautious (not in content, but in approach). The writer was much more competent and it only needed minor errors highlighted, but I'd discovered a basic fact about these groups--doing a crit requires much more trust than offering your work for one. (you can choose to ignore another's words)
It was a moderately long passage and I finished the crit(using their recommended method of inserting the comments direction into the text using capitals) and then I sat and read it several times (It is a measure of my focus that I still missed a simple typo that turned "think" into "thing"). Still not satisfied, I put it away for several hours and enjoyed the visit of all, bar one, of our grandchildren. After tea, when they'd been bathed and gone home, I sat and read it again. It was the balance between highlighting effectively what I saw to be errors and the method I had to use to achieve this that bothered me the most.
In the end, I sent it off and returned to my real work, Kayelle, having forgone five, possibly six, hours in the exercise.
It's a great life (but I sometimes wonder)