The interview process was simple and straightforward. First, HR calls you and asks you some preliminary questions, like why you're looking to leave your current firm and what your background is. Then, if they believe you're a good fit, they'll set you up to meet with the Senior Managers/Directors of the group you'll be working for. I had 3 interviews back to back to back, each about 30 minutes in length.
Typical questions are things like "Walk me through your background" and "Why are you looking to leave your current firm?" Probably the most difficult question I saw was something that is still quite common, such as "What is your greatest weakness?" The Firm is just looking to see whether or not they'd be a good fit for you and you'd be a good fit for them (my particular group interviewed in this manner, at least).
One good tip is to definitely come with questions of your own about the firm and the position itself. Since the interview is likely to be conversational, it is very important to come with questions and show that you're genuinely interested in working there. About 5-6 questions about their service lines and what the day to day will be like are good examples.