I was invited to the interview/assessment centre some months after a rejection for the same role.
After a 30' presentation of the company and the position given by the recruiters, a series of three interviews followed, mainly focused on a better knowledge of the career of the candidate and his personality profile.
No technical questions were involved, I guess they wanted to look into the inter-personal skills, as a final lunch break with other members of the team was scheduled in the end of the day. However, a deep research on the activities of Moody's Analytics is advised and you may expect some competency-based questions.
The Recruiting team and I were aware of my stronger preference for an analytical role and, although they didn't offer me a job in Client Services, they invited me for another assessment day regarding the Investor Services.