The review process (and the number of admission officials involved) varies–sometimes significantly–from school to school and sometimes even from candidate to candidate. (For instance, applications from legacy candidates, minority candidates, recruited athletes, etc. may have their files read by extra staff members.) But, yes, there is always some sort of “checks and balances” system in place. Even so, it can be a very subjective process, which means that a big dose of luck is involved. When I worked in a college admission office, it wasn’t rare for me to write “Great essay!” on an application folder, only to learn that a colleague had hated the same essay that I loved. So, if you’re born under the right star, the folks who read your essay will be all the ones who praise it. So that’s where the “luck” part comes in.
Check out The Gatekeepers: Inside the Admissions Process of a Premier College by Jacques Steinberg and A Is for Admission: The Insider’s Guide to Getting into the Ivy League and Other Top Colleges by Michele Hernandez for a behind-the-scenes peek at how two “elite” schools (Wesleyan and Dartmouth) choose their classes.