Sometimes it doesn't rise to the height of "amusing" because it's too busy being annoying, because the literary critic is holding the work to a standard of his own and criticizing it for it -- often without laying his cards on the table -- but that seldom helps because it is so often blatantly administered that you would have to be blind to miss it. It can be artistic -- vampires are symbols of communion, so this work, which portrays them as symbols of isolation is inferior -- or, worse, political -- this work is inferior because it depicts its heroine as devoted to work in order to help win the war and not for high wages, when the story was written during World War II and don't you know there's a war going on?
It can be really sad when they do not lay it on the table and it seems to be because they do not realize that the standard they are judging by is not the universal agreement of mankind. Why, when the works they judge so often "fail" or only partly succeed in their eyes, they do not consider the possibility that the writer doesn't agree with them, wasn't aiming for what they wanted, and therefore can not be said to fail or succeed at it, I do not know. (Though it makes me give a gimlet eye at their ideas. That's a fairly simple proposition. If you don't understand it, what does that say about your judgment?)
And often enough, they write as if aesthetic considerations do not exist. Why, oh why, does your heroine have an unloving family and no supportive friends? The obvious answers are that they would suck the life out of the conflict by giving her resources, and clutter up the story with redundant characters who do not advance it. There's many a literary critic to whom that would be a novel idea. Or the sharp contrast between the heroine and the villainess is not from any theory of womanhood but because they are foils to each other.