Pros
It's a great job to have if it's your first or second job out of school. You'll get the opportunity to work for big name clients with the flexibility to work several projects over the course of a few years at a time. You'll hone your skills to the point that you can get a great job anywhere. I learned more in the first 2-3 years at this company than I did in the years at my previous company. Also, the company is kept at a small size, so you'll really get to know everyone very well if you stay long enough. Great health benefits + 401k and the CEO is a great guy who cares about his employees and is mindful of maintaining a positive work environment.
Cons
This is not the kind of company you want to stay forever at. Everyone needs to leave the nest eventually. Grow and fly off when it is your time and let others have a shot at the opportunities you had. Inconsistent rule enforcement - some employees are allowed more leeway than others. It created resentment and perception of favoritism. Due to the lack of organizational structure\office\rank, you will not gain any kind of seniority regardless of how many years you've been there unless you do business development but that itself is difficult since the CEO and his partner control what projects are taken on and what you work on.