The whole process was completely relaxed. Everyone is really really nice. Even the security guards! They took a couple of us in their van to the train station just because we had just missed the shuttle, which would have come by in another 20 mintues anyway! My interview was very relaxed and conversational. To prepare for the interview, I would just suggest reviewing your app and essays. My interviewer had all my info in front of himn with stuff in my essays highlighted that he wanted to talk about. Don't stress!