Pros
An exciting company to work for with opportunities to work with some of the most prestigious clients in the world. Promotion opportunities are there for those that want them, and the office I was working in (Henrietta House) is in the heart of London. There are plenty of extra-curricular activities to get involved in and the people (by and large) are pleasant to work with.
Cons
Work/life balance is pretty dire and remote working is discouraged (you can work at home if your manager agrees, but no laptop was provided). If you get landed with a poor manager, there is little opportunity to complain as it's a very "old school" structure. I ended up deeply unhappy and depressed due to a manager who bullied me and, despite bringing it up in reviews, it was never dealt with. I couldn't leave quick enough after joining.