It's time to let loose of empty criticism. This isn't in response to anything I've personally endured lately, but I do frequent sites like Ads Of The World that showcase work and allow comments and I've worked at a place that got fed its self esteem by chopping down everyone's work so they didn't feel so bad they couldn't do it themselves. The point is, a comment like "where's the concept?" or "weak" or "I don't get it" does not qualify as a valid criticism. It's hollow dribble that's been spouted so many times, it's lost all meaning if it had any to begin with.
Criticism should be clear, constructive and specific. If there was a poor use of filters with regards to the art direction, say that. If the copy was dramatically awkward or lacked a distinct voice, say that. If the strategy didn't resonate with the advertiser's goal, say that. This sort of feedback is helpful, and can assist in improving the creative quality of work, as well as helping hone the skills of a creative professional.
However, those that insist on bashing an ad with their stamp do more to make themselves look like insightless, clueless users of adspeak jargon who are more interested in the prestige of saying "no" than creative sages committed to good work. I think too often those sorts of comments are used to prop up the users' egos and feed their need to feel superior. However, if all you can say is, "well, I just don't get it," I think you've said more truth than you know. And if that one got past you, I guess you might as well keep your stamp at your desk, because it's all you've got.