My interview experience at GLG was extremely positive. I initially interviewed for a Research Manager role. I had one 15 min phone screen, then a 30 min phone interview with the hiring manager and then got through to the third round which consisted of 7 different people interviewing me (back to back) for almost 3 hours in person. The process was pretty standard--they asked what I knew about the company, made me explain my past experience and how it would related to the job description and I got a simple case study asking me to identify contacts for a client.
However, after all this I got a phone call a week later saying that the hiring manager was a little hesitant about putting me in this role because my experience was all based in academia. She wasn't sure how I would transition to corporate but still wanted me on the team. I was offered a different role that was slightly junior (pretty equal compensation) and I accepted.