Well, I currently live in Washington so I really love the city. The interview was VERY laid back and the fellow students that interviewed were all very personable. Since their process is closed file, expect the usual tell me about yourself, why GW, why do you want to be a doctor stuff--so know those basics well. Expect a health care system related question and something about your strengths and weaknesses. They use a sheet with questions on it, so my bet is it is pretty standard.
The student interiew was much more lengthy but pretty much a conversation. The faculty interview, I had to keep the conversation going...not much of a talker and in a hurry.
Anywho, best of luck!