I have tried several on-line critique groups and forums over the years in the hopes of getting feedback to help me improve my craft. Some have been good fits, some have not.
One of the most frustrating things about getting feedback, in my opinion, is how LONG it can take. I have time frames and deadlines in my head, always. So when some forums have wait lists that are several weeks or a month long before your work gets reviewed, it gums things up for me. By that time I can have written most of a draft of a novel. I need to keep MOVING.
If you are a writer and have similar frustrations, or even if you aren't as impatient as I am, I suggest you try out You Write On. The rules are simple. You review some submissions, you get credits. You upload your submission and dole out your credits for an equal number of reviews. The best part is, there are time limits on how long you get to finish your reading assignment, which means that you get your feedback from your assigned credits within a few days. Yay!
There is also a nifty rating system where reviewers are asked to rate your characters, plot, voice, etc. on a numeric scale to give you a more objective measure of your performance. This is available after you get 3 reviews.
In addition, there is a process by which you can earn a professional review if your piece is rated high enough (I think you need 7 reviews?), and you can link a completed story to the submission to generate sales if it is available somewhere. Mostly though, I just use it to get speedy reviews and hone my own editing skills. Go write on!
Best of luck!