Pros
They hire bright minds from very prestigious schools, so in many cases your colleagues will be intelligent and exciting to work with.
Cons
Just a politically toxic culture. There is no effort at real career or personal development. There is realistically only one track in which someone is able to progress and there is no flexibility for movement across the organization. The management is not empowered to truly develop their employees other than to push for performance. The result is an impersonal environment with no room for growth. The entire company's morale is truly depressing. GLG prides themselves most on client management skills and the development of "soft skills", but really they just push young recent graduates to follow a script without actually developing any sort of true client ownership and management. The "soft skills" are quite often unmarketable elsewhere. It is a churn and burn environment that they pretend is not. All of the most talented people leave within a few years, meaning that management is mostly comprised of the people who have "stuck around"