Pros
I've been with the agency for almost six years and it's been a wonderful experience so far. The executive leadership is extremely supportive of new and non-traditional ideas and the clients are fun brands that are conducive to creative thinking. Since it's a boutique-sized agency, there are no insane hierarchical politics and departments lead by do-nothing supervisors that I've experienced with my previous employers. All the VPs and higher-ups are always accessible and foster a very egalitarian work culture.
Cons
I can't say everyone has been a joy to work with but this has vastly improved in the last few years. I appreciate how the agency has brought in folks from outside the agency world who are more open to collaboration and much less territorial.