Rigorous, back to back interviews. They use Amazon's STAR interview methodology, which is basically behavioral interviewing, see sample questions, below. (A number of folks in the team I spoke with are from Amazon.) Throughout the interview there were frequent references to Amazon as a model for excellence and results. Be ready to talk data.
For the most part a very grim-faced, robotic interview team; not a smile; they all looked insanely stressed. Good insight into what the office culture must be like. By the end of the day it was evident to me that I wasn't the person for the job, and this was not a job or company I'd want. That's OK, that's why we interview, right?
What I mind is the lack of human respect throughout the process pre and post. I've interviewed at Amazon (was rejected for one job, got an offer for another). I've got no problem with rigorous interviewing and really high standards, no problem with not getting a job. But if you're aiming to adopt Amazon best practices, deliver the goods: treat your interviewees with the same caliber of follow-through, respect and customer service you treat your customers (Amazon does); and bring your A game to the interviews. My phone screen was scheduled with the hiring manager, but I was given no context or prep - which surprised him. With one exception the interviewers were aggressive and uninformative. I left the interview with no word about next steps, and I never heard back from them. This is a senior level job and I spent a day there. Not bitter. Just extremel unimpressed.