This isn't like a peer review in a high school class -- it's much more important than that. Seasoned adults will be reading your essay looking for glimpses of your “character.” That's an old fashioned word; it means the way you develop your inner qualities: intellectual passion, maturity, social conscience, concern for community, tolerance, inclusiveness and love of learning. You should share your essay with a teacher that knows you well -- preferably, the teacher's writing your recommendation letters, as Admissions Officers look for teachers to reinforce and confirm the "character" projected in a student's essay. Ask your teachers: "Does this sound like me?" "Does this essay convey who I am?" If they answer yes, then you nailed it.
It's also not wise to share your essays on CC because another applicant could inadvertently, or on purpose, steal your idea or concept and use it in their essay.