Had the first phone interview in late November, about two weeks after submitting my application, with a Director and Senior Associate. The questions were fairly standard - why do you want to work for E3, how do you envision your role with E3, etc.
Then in early December I received a technical exercise to complete within two weeks, but which according to the instructions shouldn't take more than a few hours. Although I think that time effort estimate is highly optimistic, I thought the exercise was actually a lot of fun and much more relevant and less stressful than standard case study questions you're sometimes presented with during Consulting interviews.
Anyway, after the technical exercise is when the hiring process unravelled somewhat in my case. In the first interview I was told the overall timeline until a hiring decision would be 8 weeks and that the process would consist of 1) the first phone interview, 2) the technical exercise, 3) an on-site (or Skype for remote folks) interview , and finally 4) a conversation with a partner. After submitting my technical exercise in mid December, I was invited for another phone interview in January, which I found out only during the interview wasn't the next stage in the process, but still part of the technical exercise to ask some follow-up questions about my submission. The interviewer, a Senior Consultant, was very nice and I thought the interview as well as the technical exercise went well. After that, I heard nothing for 3 weeks so I reached out myself in late January, at which point it already had been 9 weeks since my first interview (remember the promised timeline was 8 weeks total). I was thanked for my patience and asked for more of it, so I waited for another 2 weeks until I reached out again. Another week passed until I even got an answer this time - a standard rejection email.
TL;DR: Content wise the interview process seemed well thought out and quite pleasant compared to other consultancies, but the process timeline and communication about the application status were atrocious and made me feel like they have very little consideration for you and your time as an applicant.