Pros
The work gets recognized. The people you work with are creative, talented and usually hard-working. The projects often involve new technologies or a novel approach. When it all shakes out, management usually tries to be fair and supportive, and to do the right thing. International clients allow for work to have a global impact, lots of regional localizations. A range of different types of work keeps things interesting. Dynamic mix of people leaving and arriving means there's always something or someone different to pique one's interest. Something of a start-up mentality even though it's a well-established company. The facility has improved a great deal in the last year. Fairly confident in its ability to survive, maybe even thrive during, the current downturn.
Cons
Chaotic projects make planning any work/life balance impossible. For a successful agency, getting resources is a constant struggle. Tries to do cutting edge work "on the cheap." The only way projects succeed is because key individuals work insane hours under insane conditions. Mid-level managers work too hard and carry the weight for those above and the junior employees below. There's little or no depth to the "bench." Competition among various offices creates winners (London) and losers (New York). When the client is always right, those actually doing the work get chewed up and spit out. Lack of predictability and resources makes time-off or professional development difficult to arrange. Professional development only given lip service. Long-term planning seems non-existent. Anything announced more than a month into the future is probably not going to happen, at least not as announced. Fairly high "churn" rate--your favorite people leave too soon, seems like the best are the first to leave. There's a lot more junior people lately. Recognition seems to go disproportionately to account people rather than those in the trenches actually getting the work out the door. The review process sucks and is inevitably a predetermined disappointment.