Pros
I always say it feels good to work for a company that's doing well and GLG is on something like its 10th+ quarter of consecutive growth. That success is reflected in the fast-paced, ever-changing nature of the work which (in my experience) leads to an unparalleled level of stimulation (and requires some patience, which other reviews point out). Given growth, it also feels like everyone is working towards the same thing - people are collegial and nice, and collaboration is increasing. I've had several jobs and this is one of the few places that no one raised their voice at me. And even more refreshing, people aren't just nice - they are interested... in your perspective, in your contributions, and in your life outside of work. Everyone - top down - is interested in new, big ideas, and willing to experiment. They are well-positioned to continue to succeed, and I'm very bullish about the impact they'll have on the business world. Oh, and the offices are so nice! People (especially disgruntled reviewers) mention that as a throw away point but nice offices matter and reflect GLG's investment in its employees.
Cons
Rapid growth is mostly good, but it means a lot of change and sometimes it's not implemented as seamlessly as it can be. Also, while I didn't work in client services - I recognize those jobs could be both intense (like every account management job) and monotonous, but I do believe you learn a lot of transferable skills. The reviews here that refute that are too cynical. And those who say no one goes anywhere interesting after GLG is just plain wrong - people go on to hedge funds, tech companies , nonprofits, etc. Finally, while there's a lot of diversity of background at GLG, there's not a lot of true diversity -- especially on the leadership team and board. You can't change the culture to be more inclusive, or make campus / mid-level hires more diverse if you don't fix that.