Hi,
As group host I am, of course, partial, but I can highly recommend the Intensive Critique group as we are actively seeking new blood and new things to review.

The gist of it is that you should be willing to crit three other pieces for each piece you upload to the group. In return, we tend to give relatively in-depth critiques and (because the 3:1 applies to everyone) you should get at least three considered opinions for everything you upload.

We have had a wide variety of uploads from short-stories, flashes, lipograms, scenes and chapters in a variety of genres. The group is not for the faint-hearted as Intensive Critique is more than just an aspirational title but, equally, all members are encouraged to remember that an opinion on your writing is just that, an opinion, so we try to give justification for our opinions to allow you to make up your own mind as to whether or not the crit is valid.

Either way, because of the natural ebb and flow of the writing process (I have just finished my novel and so haven't much to upload right now, for example) we are looking for new members to provide new work for review and also, as has happened more than once, to inspire the other members!

Looking forward to reading and commenting on your work,
Gaius