Pros
This company is full of 23-27 year olds, who are, for the most part, intelligent, driven folks. The company does its best to foster a supporting environment, but anyone who tells you they don't feel a fair amount of pressure is lying. Some people are cynical about it, others are really bought in--but it seems like everyone has agreed to show each other a (relatively) high amount of respect and understanding. GLG created this business model and is 100% still trying to figure this whole thing out, so it's unique in it's culture as a large company with a startup's focus on innovation.
Cons
Can be an emotional rollercoaster. Also, when you put 400+ young people in an office, it kinda feels like high school, rumor mill/drama included. You can engage with that if you want, depends on what you're looking for. The culture is pretty up or out (not consultant levels, but in the ballpark), and there are people that don't do well in the environment. GLG created this business model and is 100% still trying to figure this whole thing out, so it's unique in it's culture as a large company with startup growing pains.