Both of my interviewers were doctors, and mostly seemed to want to know more about me. My first interview was very conversational, we mostly just talked about big things in my application, e.g. the volunteer experience in my essay, my research, one other anonymous EC that would give me away instantly. My second one was more like an interview, with the doctor asking a few tougher questions that weren't just variations on "Tell me about yourself." The second one seemed more formal than the first, but neither one was very intense.