The interview was less than 5 minutes, maybe three. Asked how many kids I had, their names, where I live in the U.S., how did we meet, where did we first vacation together, things like that. Nothing she didn't already know or hadn't prepared for.
Now, there was a guy with seemingly his fiancee or wife and two kids who had it way tougher. She was being questioned for over 15 minutes, rifling through paperwork to show, etc. Given how easy our situation was, I was guessing that there was either documentary evidence that she had failed to produce or she had some wrinkles in her background that also got extra scrutiny. I have also read that folks with very common names (e.g. Maria Gonzalez) could face a bit more scrutiny.
In any case, the satisfaction and joy at the end of the interview of hearing that the petition was officially approved was priceless. We left with big smiles on our faces. It was also nice to see countless other couples with those same smiles as they walked away from their interview booth.