Casual, and not so hard. There were several senior level designers attended the interview, and they introduced the office, team, their current works. Then we talked about your past experience and your expectation.
I applied through an employee referral. The process took 2+ months. I interviewed at AECOM in Jun 2010
Interview
The interview process was a little unorganized. I had a lot of trouble connecting with my contact person before and after the initial phone interview, but whenever we spoke things were very positive. The office was very impressive in terms of address, but pretty stale and corporate like inside. Unfortunately I did not get to meet any of my prospective co-workers. The interview seemed to go very well. I had a lot in common with the interviewer who would be my direct supervisor. Several weeks passed without communication till I received an application and the offer packet.