Thorough, 5 round interview. First few with HR and a manager to ask about you and your motivations.
Then comes the really enjoyable part, the on-site interview rounds with some of the future colleagues who says "the interview begins when we reach the bottom of your knowledge and progress on to uncharted territory."
It was really enjoyable, my best to date interview process. As I got hired, I get to know they enjoyed it too. It was a few interesting, yet technical discussion.