Total nightmare.
We led with a phone screen, which went fine.
When I arrived at the office, I was immediately ushered into a conference room, and the door shut. No HR person to greet me, no recruiter, nothing. After standing there for literally five minutes with no idea what was going on, six people filed into the room. This was a group interview, where they would rapid-fire ask me questions. It was all I could do to keep up.
This was very stressful, but a totally valid interview style. I don't fault them for that.
After about 20 minutes, they got up and left the room, and I was on my own again. Maybe 10 minutes later, an engineer comes into the room and asks me to design a relatively complex system. I come up with a starting point, but either I didn't explain it well, he didn't understand what I was saying, or he just wasn't interested in any solutions other than his. I managed to make some progress, but eventually ran out of time. He seemed in a bad mood the whole time; maybe this was an off day or maybe he was just a disagreeable person, I don't know.
After he left, I was on my own for another 10 minutes or so, so I finished the problem on the whiteboard, since I had nothing else to do.
When the next interviewer came in, he glanced at the board and said it looked right, so I at least felt better about that problem.
The second interviewer was much warmer, and the question was actually fun. We made our way through the question, and were just wrapping up when the head of engineering came in.
"You don't need 2 variables, you can just use one.", he said.
"Ok, let me get a working solution then I can optimize.", I replied.
"No, do it with one variable."
So I tried to make that change, but that required rewriting a chunk of code that was already small on the whiteboard. I tried using a different color pen, but it was still impossible to re-write before the buzzer sounded.
They both left, and I was on my own for perhaps 15 minutes. I could hear people in the hall asking "Where is he? What's his cell? Did he say if he was going to lunch?"
Basically, they couldn't find the third interviewer, so they just decided to vote no on me. The head of engineering came in and told me it was a no-go, and asked if I wanted to know why or not. I said sure, feedback is always good, and he basically started talking about how I was doing everything too slowly.
Horrible experience. This was a couple years ago; maybe things have changed, but back then I would advise everyone to stay far, far away.