Pros
The company has seen a lot of growth in the last year especially, and continues to aggressively seek new opportunities. This means lots of opportunities for employees to branch out, take on new challenges, learn, and find ways to stand out. The company's culture has improved as efforts have been made to have more events for employees, upgrades have been made to the office, and other small perks here and there. I like the people I work with, and people seem to generally look out for each other.
Cons
The work can be very demanding and require long hours, and there isn't much guarantee of when that will be, since some kind of client need is usually the basis, and the company has little control over that. Working late into the night or on the weekends is not uncommon. It can also be very uninspiring or unexciting work, but that's just the nature of advertising, at least when it's not your own brand you're working on.