I first had a phone interview with the VP of Human Capital (HR). She was really nice and just asked me a lot of questions about me and my story (i.e. why I chose my school/major, what interested me in the position, where I want to go).
From there, I had another phone interview with an Account Manager, someone who had recently been promoted from Account Associate. Again, very very nice and was interested in my story. She did ask me a few more questions about my skill set, what I was looking for in a company, and where I saw myself in 5 years.
The next step was an in-person interview in Waltham. They flew me out and arranged for me to stay in a very nice hotel in downtown Boston. I ubered to the office the next day and met with a variety of people. My first two meetings were about 45 mins with Account Directors, then an Excel case with a General Manager. The case is pretty basic, but they are more interested in how you approach the problems and if you are familiar with excel formulas. Finally, I went out to lunch with the Associate who did my phone interview.
Overall, it was an easy to average difficulty interview. I can't stress how NICE everyone I met was. It's clear that they really care about finding the right fit for you and the company.