Pros
By far the best part of C-4 is the people, as many of the other reviews state. You never have to worry about asking someone for help or advice as almost everyone is friendly, helpful, and insightful across all teams (account management, social, creative, and programmatic). Another major pro of working at C-4 is the experience that you gain. From Google Analytics to AdWords to reporting tools and client communication skills you will master a slew of programs and abilities that will make you extremely valuable to multiple employers.
Cons
One major con is the pay, which is low, even for the advertising industry. Having such a low salary makes it difficult to stay loyal to the company when working full time barely pays well enough to make rent/ mortgage each month. Unless you prove yourself by working hard and get on the right people's side your salary bump when you do get promoted will not make much of a difference. In addition to the low salary, those in the executive suite are very out-of-touch with the rest of the company. They always ask the account management team for referrals from existing clients, but then give the AM a hard time and will often low-ball when compensation time rolls around. Finally, there is a major problem with clients saying "jump" and the company asking "how high?" Client retention is obviously important, but management will often ask AMs to go to extreme lengths to please a client, often to the point where it has negative connotations on existing, happy clients because the goals of the happy clients have to be pushed to the side to make way for the angry client.