"Are all metaphor essays bad?"
First, a quick review. A metaphor is just an assertion that one thing is like another thing. In the college essay context, the usual approach is to try to argue that the student is like some object. For example, a roller coaster could be a metaphor for the student's life.
To answer the question, no, not all metaphor essays are bad. But all random metaphor essays are bad. A random metaphor is one that compares you to something outside your every-day experience. If you compare your life to a roller coaster even though you've never ridden one, roller coasters are not your best metaphorical option. I sense the attraction of random metaphors is the belief that if we could just find the right, clever metaphor, we'd win over the reader. But there's no such thing as a magic metaphor (or topic) that will, simply by appearing in your essay, stab the admission officer with wonder: "Oh my gosh! This applicant's a spork - multi-functional!" A random metaphor seems out of place, like an unattended elephant ambling down a city street.
For a metaphor to work, it has to be authentic, not random. But finding authentic metaphors is easy. Pluck them from the scenes - the particular moments - you'll be describing in your essay. If I'm writing about writing (my curse, apparently), then maybe the staple remover on my desk is a metaphor for my outlook on editing; I disassemble words and reassemble them in a better order. Or the aluminum Dr. Pepper can is a metaphor for my ideas: recycled. So long as you draw the metaphor out of your scene instead of imposing the it onto your essay, your metaphor will be authentic.
Good luck writing!
Jon Perkins holds a B.A. in English from Stanford University and a J.D. from Harvard Law School. He helps students with their college, law school, and medical school applications.