I agree with John completely: the purpose of critique is to learn
something that will help you improve your skills. What works, what
doesn't work. And importantly: why?
The point about the context is a valid one, and it will be helpful if people who post images would include as much background information as possible.
That being said, I think many of the posts here have been quite good in that respect. Maybe the initial post was a bit thin, but in most cases the poster got on to the idea and posted more details after a few comment.
I think this forum is very valuable.