Pros
Obviously it's a really well recognised brand, and if you make a good impression on people with the right people and/or end up in a good team, you can get involved in quite interesting work.
Cons
Despite all the HR rhetoric around "we do everything, so you can have multiple career paths within the same company" the reality is that business need is absolute number 1, above investing in their people, developing logical approaches to client relationships etc. There's a huge disconnect between the product recruiters sell you (6 month rotations in different areas, develop your skills, opportunity for exposure to strategy work, analytics) is extremely different from the reality (a lot of need for technical or administrative grads, account partners are only interested in the skills you have and will keep you in a role for 12 months+ to use them). Resource management is so convoluted that in practice the only way to get on to projects is to know the right people, which results in a bit of a "boys club" atmosphere on some accounts. And obviously lots and lots of systems that you have to go through for everything from reclaiming expenses to trying to be promoted, none of which seem to integrate at all.