It was not bad at all. We showed up about 30 minutes before our interview. We were called in about an hour after our appt time. The officer apologized as their was a big back log they were dealing with. She asked for the documents listed in the interview letter. She went through the file, and asked about basic stuff. She asked how we met, joint documents, pictures, things of that nature. It was a piece of cake. She wrote down notes as we answered her questions.
In the end she gave us an RFE for a document she needed. She apologized that she could not approve us on the spot, but once she received the document we would be approved. 2 Weeks later our online status stated our application(s) had been approved. If you have everything they ask for, and they are satisfied with your answers, more then likely they will approve your i-130 & i-485 on the spot.
The officer was extremely nice in that we had filed my wifes petition under her maiden name. When we sent in the required document, we sent a long a letter requesting her green card be made with her married last name. Sure enough when we received the green card, it had her married last name. It truly is a painless process. The worse part is the wait time to get the interview. Hope that helps.