Pros
The staff here genuinely care about the work they do, and the people they work with. There is a great work-life balance, and the management will always do their best to help you out wherever possible. Some great projects pass through the doors, far more interesting work than a 'typical agency' might expect to see. Innovation is encouraged, and ideas are given the space to grow. Great office atmosphere with plenty of work space, quiet areas, siloed booths for calls and small meetings, Xbox, table tennis, etc. Helps to switch off during down time. Doesn't really feel like work, and never dread going in.
Cons
Ideas and innovation is encouraged, but you are expected to own and push them through. Agency work can often be fast paced with looming deadlines, so it's important to be able to (sometimes) work quickly but maintain standards.