First off, the people were great. Friendly, smart people.
The first round interview was fairly casual and almost entirely focused on the two cases (with a bit of chit-chat for each interviewer, but no real resume questions). I messed up on a bit of math in my second case, but still got passed onto the second round. The interviewers for this part were consultants.
For the second round, I was flown to the office I was actually applying to, and the flight booking & everything was really easy, so that was nice (and they reimburse you for everything). In the second round, there were two case interviews and then a third interview focused entirely on resume & my skills/experiences. The interviewers here were managers & partners, so a bit more intense but still very friendly.
Overall, great experience. Bummer I didn't get the internship, but I had a lot of fun regardless and will be applying again.