Brown truly does a holistic review in that once you clear the numbers hurdles we're more interested in who you are than making decisions on people via X > Y b/c 39Q > 34P logic. That being said, I fully recognize that this makes the process a bit more stressful at Brown specifically, because it's hard to know what about yourself really makes you shine. The following post is not meant to stress, merely to help those who are able to read it in light of the record number of applications we've received this year (2500 and counting, last I checked).
Being on the other side of the process, I can truly say that the biggest thing to get an interview this year is to figure out how to make yourself interesting. If you don't have the kind of GPA or MCAT to make people sit up and pay attention (which most in the pool don't, and *that's just fine*), make sure your personal statement singles you out. Read it as a disinterested third party, would *you* want to meet the person described? Call out interesting life experiences, interesting research. If you met someone at a cocktail party or were meeting someone at a random party, what would make them think you're different, interesting, and someone they want to talk to?
As far as a letter of interest goes, *if you write one,* that would be a clear place to make your point again. And if you haven't already made it clear, what is it specifically that makes you interested in Brown? We accept a relatively high proportion of the people we interview, so in some ways we already want to know that there's a reasonable chance you'll attend if you get an interview. Do you have friends or family in the area? Do you love Providence (and why)? Is it something about our curriculum (hint, special concentrations are available lots of schools, talking only about those does not do as much to single you out as you would think), our student body, or the opportunities you'll have while here?
