Not to diminish the importance of the topic, we've had other discussions about critiques here, and I think they've all been fairly inconclusive. Giving someone else a critique of their work, or even just a single photograph, is an art in itself. Not everyone is good at it, as the experience of many critique-ees would suggest.
Perhaps the best critiques are those in which a level of interactivity is possible - that is, a discussion of the image (or, body of work), and the intent or motivations behind it, rather than simply impressions without context.
I think it's also important to put critiques in the context of being just one person's opinion - even if that one opinion is important to you. Photography, like most arts and/or crafts, is a means of communication. Not everyone will get the same message, or have the same impression of an image. Thus, the relevance of the critiques is perhaps better viewed as a pool of comments, enabling you to determine whether your "communication methods" are working for a majority of people. Even then, however, that has to be balanced with the desire for self-expression.