Currently I'm not listening to very much, although I check in to see the activity on a regular basis. It kinda feels like a community to me...like going and sitting around in the student union/coffee shop in college and watching everybody....
As far as coming up with constructive criticism. Some days I have lots to say and other days (especially at present when there's so much drama going on in my family, using up so much of my energy) I can barely think of a thing.
Specifically, though, production is definitely not my thing, so I seldom provide feedback on it. Except for really obvious things, like if one part is drowning out everything else. Plus, unless the person posting asks for feedback on production, I figure the whole idea is to give feedback on the song itself--the construction of the words, how the words and music fit together, that kind of thing. Prosody is important to me. I listen to see if the rhythm of the musical phrasing fits the rhythm of the words. For instance...the word "frustrated". Does it come out like it should, that is: "FRUS-tra-ted"? Or is it more like "frus-TRA-ted" (a popular singer did that a couple years ago or so, and it still rubs me the wrong way). And if the topic is happy, does the music sound happy? When the words talk about, say, "low places", does the pitch drop down for the word "low"? Do the words flow in a natural way or does the songwriter use "yoda-speak"?
And, since the idea is to provide constructive criticism, I try to come up with examples of ways to improve the problems I perceive. Sometimes people want things the way they wrote them for a reason, so I try to remember to mention all my ideas for improvement are based on my personal opinions and they may not agree. And that's okay.
By the way, when people review my work, I really like it when they find a lot of problems for me to work on. It helps me get better and, for some reason, I just like being able to "sink my teeth" into studying their remarks and using them to get deeper into the workings of my song.
I hope this is at least a little helpful....
Vicki