I once received a critique that went, "There's something wrong in the second half." My reply was, "Can you be any less specific?" That's the kind of stuff that's maddening.
But good criticism is invaluable. Some of the best notes I've received were the ones that pointed out a central flaw in my work, which often forced me back to square one but got me to write a much better script.
And good criticism can open doors. A few years ago a producer I knew was having difficulty getting notes on a script from the director attached to the film. Since he wanted a rewrite done, he asked me if I'd read the script and give him notes. So, I did, and gave him 25 pages of notes on the 130ish page screenplay. His response was, "These are the best notes I've ever seen! Would you want to do the rewrite?" so, we made a deal, he paid me, and I did the rewrite. I think the thing that got his attention wasn't just that I said what was right and wrong, but where things were wrong I had very specific and practical proposals on how the issues could be fixed...plus I also suggested how to cut unnecessary characters and scenes and settings in a way that also lowered the production costs. I consider that a good critique.