Pros
Fun people, good work/life balance, cool office space, great location. Also get the week between Christmas and New Year's off which is nice. Can work remote if you need to. Often have agency lunches, birthday celebrations or other fun cultural/team bonding events.
Cons
Client diversity is lacking, projects can be bland because client budgets aren't super big and education (i.e. attending conference)s isn't always consistently encouraged and/or financially supported and it should be.