Pros
Agency work allows you to have a high turnover of projects, so you can constantly refine your fundamentals and explore new technologies. Coworkers all had a solid grasp of their area and generally worked well together to get things done on time.
Cons
A solid lack of management and a lack of good work ethics far outweigh any of the positives. Project managers have no prior industry experience and double duty as QA. Management is willing to expand scope on a project, upping the requirements for producers, without changing deadlines. Former employees were cheated out of part of their salary upon leaving the company. Management is hard focussed on the bottom line (their bottom line) and don't care too much how that affects employees as they're always willing to get more - expect a high turnover rate.