Pros
The people are generally nice and it's possible to maintain a good work-life (if you prioritize it yourself). The agency has some cool clients and pretty solid benefits: decent healthcare; free access to houses in the Catskills for personal vacations; the 401k match is 'discretionary' but it was never less than 5% and once was 10% in the 3.5 years I was there.
Cons
There is a sense that certain divisions aren't valued as much as others. We were consistently told we weren't getting the raises we wanted because our division wasn't performing up to the CFO's standards. I think this is in large part due to the fact that some sectors (e.g. travel) are never going to make as much or have the same % of ROI as tech or healthcare. So it felt like being punished for working in that particular division. This might have something to do with a newish CFO as well as the constant company acquisitions, which also led to some resentment because the company could afford to buy other firms for millions of dollars but couldn't give reasonable raises to their employees. It's possible you could face similar issues at other agencies, but I do think it leads to people taking other job offers and was definitely a factor in my leaving Finn for another agency.