This thread proved to be very helpful when I was preparing for my interview so thought I'd share my experience as well, in hopes of helping others going through the same process!
The overall experience was very smooth and straightforward. My interview time was for 9:00am and I arrived at the consulate around 8:30am. They ask to see your passport at front desk and give you a laminated handout with a number on top and a list of documents you need to prepare for the officer before being called. After that, you go through security - recommend the ladies to carry small purses with minimal items in it. If you decide to carry your phones, they will be held at security until you have completed the interview. One girl carried her backpack with her and was asked to go drop it off to a storage location (15mins away from the embassy) and then return back! After security you will be instructed to follow steps down through the corridor and take the elevator up to 19th floor.
On the 19th floor, there will be 2 sides, one for immigrant and the other for non-immigrant visa. The immigrant visa side will be right in front as soon as the elevator door opens (there is also a sign hanging from the ceiling on that side). Once you take a seat, you will want to take the time to prepare your documents according to the instructions on the handout, whilst waiting for your number to be called. I was between #20-25 and when I arrived they were calling out #14-15 I believe. I was lucky to be surrounded by a few people who were friendly enough to strike a conversation, so it helped calm my nerves and let time pass by quickly as well. You will want to hear the numbers called out carefully because they call out names of people there for non-immigrant visas simultaneously and sometimes the speaker was very faint, so we were often not sure who they were calling for! However, for the most part it seemed that the immigrant visa numbers were being called out clearly. Regardless, pay close attention!
Around 9:45-10am my number was called to the counter where they basically want to see all the originals of documents you submitted, anything else they requested from you before the interview, verify the stuff and take your fingerprints. After that, you are advised to return to the waiting area until you are called again. I only had to wait for around 5-10 mins before I was called again and this was the official interview. The lady was super nice, she asked a few basic questions, such as how my husband and I met, how long we had known each other, what he does, where he lives and a few things about me - countries I had lived in, education background etc. Seems like they just want to verify the information you provided is consistent and true. That was about it. After that, she did a final document check and returned any originals they had retained, gave me a blue approval letter and kept my passport, and told me I should receive it within 1-2 weeks! At this point, I requested if there was any way to expedite the return because we have a trip booked for the week after (took proof) and she said they usually try their best to return it within 1 week, but they cannot promise anything!
My visa was issued 1-2 days later, and was shipped out on the 3rd day after my interview (on a friday). Currently expecting receipt by Monday so hoping it arrives without any issues!
PS - I had made a mistake in my case number while registering for courier services so was very worried it would affect the return of my passport, but it did,n't seem to impact anything. However, you cannot change/correct the info once you have submitted it and your interview appointment is booked and the USVISA services apparently can't change the info for you either, so just double/triple check all the info while registering for courier service! I must have quadraple times checked my info but somehow just missed this one small detail and instead of feeling relieved and super happy about the approval I spent the next day or two worrying about the return of my PP!
Best of luck!!