Pros
I spent nearly 4 years working at GLG and it was a great experience. It is a vibrant company, growing rapidly, with smart management and good morale amongst its employees. The NY office has a cutting edge feel, with radical architecture and lay-out, plus a terrific barista, that give the environment the exciting feel of a high-tech start-up that has arrived. The flexibility that GLG offers its employees to be themselves and have a good work/life balance as they achieve at work is the best I've seen. I am musician outside of work and I was always supported by management and my colleagues and this meant a lot to me. While competition has gotten stronger it was rewarding to work for a company that the market recognized as a cut above the rest. GLG is an incredible place to grow your career and network. I grew directly from learning from my managers, who were fantastic people, and my colleagues, who were smart and intellectually curious.
Cons
GLG is growing rapidly and the pace of change can feel intense, and perhaps that's not for everyone. But if you're a driven person it shouldn't be a bad thing.