Pros
I get to work on diverse set of projects, with very smart coworkers. The management structure is very flat, so there's little in the way of micro-managing; you have a large say in how you manage your time and prioritize your own projects.
Everybody has their own office, so it's easy to concentrate and get work done. At the same time, though, most people leave their doors open, and everyone is approachable amenable to discussing each others' projects. We aren't divided into competing 'teams' or 'departments', so all of the incentives encourage collaboration between colleagues.
Cons
You can certainly gain responsibilty as you continue to work at TGS, and your total compensation will reflect this. However, since the management structure is so flat, you won't get increasingly impressive titles to match your responsibilities. In fact, you're never really given an official title at all.