GLG is not a place to stay, if you're smart.
1) GLG lies to prospective employees. Just look at the job descriptions. "Research manager" really means that you're an order taker who will do the same task 10-12 times/day. You'll also be a secondary salesperson responsible for the growth of an account while the primary salesperson berates you for making decisions with limited information or support. It doesn't matter if your decision was actually good for the company/client. "Engagement coordinator" is really call scheduling. You're going to spend your day asking for availability, scheduling, re-scheduling, cancelling same-day, and dealing with the backlash from people who feel like they're in some dystopian novel. The only teams that seem to exercise any real skills are the strategic projects and surveys teams, but even they spend most of their time just dealing with hyper (narcissistic?) egos in the "research manager" and "business development" teams.
2) GLG is an excellent case study in the Peter Principle. There are VPs galore, but what do they do? They certainly don't help those below them succeed. They go to meetings to misrepresent the morale of the company or even the day-to-day workflow. They got to where they are not because they are examples of excellency, but because they managed not to find more meaningful/skills-based work elsewhere as the smart and talented left. They are the salt that remains when you boil a pot of water too long.
3) The culture is poison. There is a fight for who gets to be "client facing," a recognition system that thanks only the VPs who sit on the shoulders of those actually doing the work (research managers, associates, survey team, strategic projects, etc.), a broken compensation system (managers often make only a few thousand more/year than their subordinates, the move from jr. to sr. associate is a pay-cut, disappointing bonuses, and yearly compensation talks that end with "you'll get a raise when you get promoted!"), all with general bad attitudes towards teamwork. There is drama galore and gossip abounds, but when you raise it to management suddenly YOU are the one with the bad attitude. You don't stress out about your work, you stress out about the people who make your work life miserable. Even those with the best attitudes and work ethic have it beaten out of them.
4) Very few skills are developed after the first year. Yes, I learned very quickly how to work with tough people (tough clients, sure, but mostly tough coworkers!) and how to communicate effectively. But what next? One is not able to explore new research approaches because GLG is a client deferential company that is really afraid to engage with research. "Managers" are misnomers because they're just ways to deal with the huge classes of bright-eyed and bushy-tailed graduates happy not to be working at a coffee shop. Little management happens even at the high levels. What are you left with? A shell of your ambitious self.
5) Work/Life balance is hard. It's not that the job is so intricate that you must obsess over details into the late hours, it's that there's just so much stuff to do and not enough people (or adequate automation) to do it in a reasonable amount of time. Some of that is cyclical (for example, "earnings season" means that clients need to do more research) but even in the "slow" times it's not unheard of for people to be working 50-60 hours just to get through their to-do list. This contributes to many of the issues in #3, where people are so overloaded even the most pleasant with great work ethics become difficult to work with.