Pros
They give you a lot of responsibility and almost completely hire employees right out of college. You can work on accounts with big names and really learn the business. They really try to make it a fun work environment and they do try to do company wide activities.
Cons
Firstly, many of the supervisors tell the employees to come and rate the company high on here, which seems unethical to me. Secondly, much of upper management can be over-bearing and there can be little respect for employees, management is usually far older than the average employee so it can be a strange complex. The ads they produce also aren't the best ones, you get told over and over again "it pays the bills", so there's not much pride in the work. Since they hire directly from college, there's a good amount of nepotism, cliques, low pay, and grievous mistakes made by inexperience...this in turn, makes HR almost like college RAs. There is a lot of turnover with employees, a lot. Their business model is to hire cheap younger employees, then make them work at a high volume and not so great quality. The model is good for now but it's not something that will last in the market for years to come, it will eventually plateau.