It was surprisingly simple, the interview was simply a review of the documents and probably no more than five (5) questions were asked. All-in-all the interview probably lasted 10 minutes and it wasn't even in a room, it was just walking up to a counter and speaking to an official.
Take in to account, however that my wife was in the U.S. as a student for almost 6 years and there was plenty of evidence supporting our relationship.