David Foster Wallace's English 170R syllabus includes some fantastic guidelines for providing useful peer review - and it's fully applicable to screenplays (scroll down): http://www.salon.com/2014/11/04/david_foster_wallaces_amazing_fiction_syllabus_we_can_talk_about_whatever_you_wish_to_%E2%80%94_provided_that_we_do_it_cogently_and_well/

Great article! I once belonged to a now defunct online fiction writing group and it was a rare day that someone actually provided others with a true constructive critique. Mostly, it was "I liked it" or "It didn't work for me," neither of which is helpful at all. On occasion, there would be the snarky comment, starting flame wars which ultimately killed the group. For me, if someone's going to critique my work, I only ask them to do one thing: read the piece for content before writing a detailed, point by point, essay on technical issues or worse, a simple "I liked it" or "I hated it." If the work doesn't stand on its own as an entertaining narrative, than it has bigger problems than a few failed bits of dialog or unnecessarily passive prose or grammar nits. That is, do what I try to do -- turn off the editor brain for a second and read the damn thing like a reader would!

Josh, thanks for that. Excellent resource, one I've downloaded for use with my teaching and writing.

Michael, you've hit on a big part of it: Going beyond the safe zone of "I liked it" or the shallow zone of "I hated it". Why? What about this scene or story worked / didn't work for you? Honest assessment of the material combined with a genuine effort to provide suggestion to make the material better. It's a win-win, both the critiqued writer and the writer making the critique because as noted, per the latter, that's a key path to how a writer develops critical analytical skills.

Once again, Scott, you don't tell us what to do, but show us how to think; outstanding--thanks!